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feat: add solutions to lcci problem: No.16.20 (doocs#1048)
16.20.T9
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lines changed

‎lcci/16.20.T9/README.md

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## 题目描述
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<!-- 这里写题目描述 -->
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<p>在老式手机上，用户通过数字键盘输入，手机将提供与这些数字相匹配的单词列表。每个数字映射到0至4个字母。给定一个数字序列，实现一个算法来返回匹配单词的列表。你会得到一张含有有效单词的列表。映射如下图所示：</p>
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![](./images/17_telephone_keypad.png)
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<p><strong>示例 1:</strong></p>
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<!-- 这里可写通用的实现逻辑 -->
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**方法一：逆向思维**
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我们考虑一种正向的解法，遍历字符串 $num$ 中的每个数字，将其映射到对应的字母，然后将所有的字母组合起来，得到所有可能的单词，再与给定的单词列表进行比较，若单词在列表中，则将其加入答案。这种解法的时间复杂度为 $O(4^n)$，其中 $n$ 为字符串 $num$ 的长度，显然会超时。
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我们不妨考虑逆向的解法，遍历给定的单词列表，对于每个单词 $w$，判断其是否能够由字符串 $num$ 中的数字组成。若能够组成，则将其加入答案。那么问题的关键在于如何判断一个单词是否能够由字符串 $num$ 中的数字组成。我们只需要遍历单词 $w$ 的每个字母，将其还原为对应的数字，逐个与字符串 $num$ 中的数字进行比较，若相同，则说明单词 $w$ 可以由字符串 $num$ 中的数字组成。
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时间复杂度 $O(m \times n)$，空间复杂度 $O(C)$。其中 $m$ 和 $n$ 分别是单词列表的长度和字符串 $num$ 的长度；而 $C$ 为字符集大小，本题中字符集大小为 $26$。
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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class Solution:
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def getValidT9Words(self, num: str, words: List[str]) -> List[str]:
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def check(w: str) -> bool:
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return all(d[c] == num[i] for i, c in enumerate(w))
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d = {c: d for c, d in zip(ascii_lowercase, "22233344455566677778889999")}
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return [w for w in words if check(w)]
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```
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```python
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class Solution:
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def getValidT9Words(self, num: str, words: List[str]) -> List[str]:
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trans = str.maketrans(ascii_lowercase, "22233344455566677778889999")
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return [w for w in words if w.translate(trans) == num]
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Solution {
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public List<String> getValidT9Words(String num, String[] words) {
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String s = "22233344455566677778889999";
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int[] d = new int[26];
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for (int i = 0; i < 26; ++i) {
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d[i] = s.charAt(i);
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}
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List<String> ans = new ArrayList<>();
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int n = num.length();
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for (String w : words) {
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boolean ok = true;
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for (int i = 0; i < n; ++i) {
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if (d[w.charAt(i) - 'a'] != num.charAt(i)) {
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ok = false;
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break;
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}
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}
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if (ok) {
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ans.add(w);
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}
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}
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return ans;
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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vector<string> getValidT9Words(string num, vector<string>& words) {
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string s = "22233344455566677778889999";
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int d[26];
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for (int i = 0; i < 26; ++i) {
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d[i] = s[i];
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}
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vector<string> ans;
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int n = num.size();
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for (auto& w : words) {
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bool ok = true;
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for (int i = 0; i < n; ++i) {
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if (d[w[i] - 'a'] != num[i]) {
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ok = false;
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}
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}
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if (ok) {
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ans.emplace_back(w);
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}
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}
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return ans;
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}
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};
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```
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### **Go**
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```go
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func getValidT9Words(num string, words []string) (ans []string) {
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s := "22233344455566677778889999"
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d := [26]rune{}
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for i, c := range s {
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d[i] = c
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}
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for _, w := range words {
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ok := true
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for i, c := range w {
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if d[c-'a'] != rune(num[i]) {
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ok = false
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break
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}
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}
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if ok {
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ans = append(ans, w)
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}
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}
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return
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}
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```
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### **TypeScript**
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```ts
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function getValidT9Words(num: string, words: string[]): string[] {
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const s = '22233344455566677778889999';
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const d: string[] = Array(26);
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for (let i = 0; i < 26; ++i) {
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d[i] = s[i];
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}
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const ans: string[] = [];
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const n = num.length;
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for (const w of words) {
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let ok = true;
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for (let i = 0; i < n; ++i) {
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if (d[w[i].charCodeAt(0) - 97] !== num[i]) {
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ok = false;
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break;
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}
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}
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if (ok) {
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ans.push(w);
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}
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}
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return ans;
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}
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```
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### **...**

‎lcci/16.20.T9/README_EN.md

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<li><code>words[i].length == num.length</code></li>
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<li><code>There are no number 0 and 1 in num</code>.</li>
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</ul>
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## Solutions
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<!-- tabs:start -->
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### **Python3**
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```python
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class Solution:
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def getValidT9Words(self, num: str, words: List[str]) -> List[str]:
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def check(w: str) -> bool:
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return all(d[c] == num[i] for i, c in enumerate(w))
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d = {c: d for c, d in zip(ascii_lowercase, "22233344455566677778889999")}
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return [w for w in words if check(w)]
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```
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```python
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class Solution:
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def getValidT9Words(self, num: str, words: List[str]) -> List[str]:
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trans = str.maketrans(ascii_lowercase, "22233344455566677778889999")
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return [w for w in words if w.translate(trans) == num]
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```
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````
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### **Java**
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```java
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class Solution {
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public List<String> getValidT9Words(String num, String[] words) {
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String s = "22233344455566677778889999";
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int[] d = new int[26];
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for (int i = 0; i < 26; ++i) {
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d[i] = s.charAt(i);
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}
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List<String> ans = new ArrayList<>();
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int n = num.length();
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for (String w : words) {
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boolean ok = true;
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for (int i = 0; i < n; ++i) {
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if (d[w.charAt(i) - 'a'] != num.charAt(i)) {
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ok = false;
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break;
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}
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}
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if (ok) {
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ans.add(w);
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}
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}
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return ans;
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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vector<string> getValidT9Words(string num, vector<string>& words) {
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string s = "22233344455566677778889999";
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int d[26];
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for (int i = 0; i < 26; ++i) {
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d[i] = s[i];
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}
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vector<string> ans;
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int n = num.size();
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for (auto& w : words) {
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bool ok = true;
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for (int i = 0; i < n; ++i) {
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if (d[w[i] - 'a'] != num[i]) {
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ok = false;
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}
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}
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if (ok) {
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ans.emplace_back(w);
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}
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}
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return ans;
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}
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};
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```
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### **Go**
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````
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```go
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func getValidT9Words(num string, words []string) (ans []string) {
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s := "22233344455566677778889999"
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d := [26]rune{}
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for i, c := range s {
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d[i] = c
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}
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for _, w := range words {
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ok := true
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for i, c := range w {
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if d[c-'a'] != rune(num[i]) {
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ok = false
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break
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}
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}
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if ok {
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ans = append(ans, w)
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}
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}
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return
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}
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```
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### **TypeScript**
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```ts
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function getValidT9Words(num: string, words: string[]): string[] {
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const s = '22233344455566677778889999';
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const d: string[] = Array(26);
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for (let i = 0; i < 26; ++i) {
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d[i] = s[i];
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}
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const ans: string[] = [];
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const n = num.length;
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for (const w of words) {
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let ok = true;
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for (let i = 0; i < n; ++i) {
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if (d[w[i].charCodeAt(0) - 97] !== num[i]) {
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ok = false;
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break;
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}
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}
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if (ok) {
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ans.push(w);
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}
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}
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return ans;
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}
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```
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### **...**
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‎lcci/16.20.T9/Solution.cpp

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class Solution {
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public:
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vector<string> getValidT9Words(string num, vector<string>& words) {
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string s = "22233344455566677778889999";
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int d[26];
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for (int i = 0; i < 26; ++i) {
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d[i] = s[i];
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}
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vector<string> ans;
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int n = num.size();
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for (auto& w : words) {
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bool ok = true;
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for (int i = 0; i < n; ++i) {
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if (d[w[i] - 'a'] != num[i]) {
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ok = false;
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}
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}
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if (ok) {
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ans.emplace_back(w);
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}
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}
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return ans;
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}
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};

‎lcci/16.20.T9/Solution.go

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func getValidT9Words(num string, words []string) (ans []string) {
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s := "22233344455566677778889999"
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d := [26]rune{}
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for i, c := range s {
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d[i] = c
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}
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for _, w := range words {
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ok := true
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for i, c := range w {
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if d[c-'a'] != rune(num[i]) {
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ok = false
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break
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}
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}
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if ok {
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ans = append(ans, w)
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}
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}
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return
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}

‎lcci/16.20.T9/Solution.java

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class Solution {
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public List<String> getValidT9Words(String num, String[] words) {
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String s = "22233344455566677778889999";
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int[] d = new int[26];
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for (int i = 0; i < 26; ++i) {
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d[i] = s.charAt(i);
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}
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List<String> ans = new ArrayList<>();
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int n = num.length();
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for (String w : words) {
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boolean ok = true;
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for (int i = 0; i < n; ++i) {
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if (d[w.charAt(i) - 'a'] != num.charAt(i)) {
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ok = false;
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break;
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}
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}
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if (ok) {
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ans.add(w);
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}
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}
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return ans;
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}
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}

‎lcci/16.20.T9/Solution.py

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class Solution:
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def getValidT9Words(self, num: str, words: List[str]) -> List[str]:
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trans = str.maketrans(ascii_lowercase, "22233344455566677778889999")
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return [w for w in words if w.translate(trans) == num]

‎lcci/16.20.T9/Solution.ts

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function getValidT9Words(num: string, words: string[]): string[] {
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const s = '22233344455566677778889999';
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const d: string[] = Array(26);
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for (let i = 0; i < 26; ++i) {
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d[i] = s[i];
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}
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const ans: string[] = [];
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const n = num.length;
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for (const w of words) {
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let ok = true;
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for (let i = 0; i < n; ++i) {
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if (d[w[i].charCodeAt(0) - 97] !== num[i]) {
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ok = false;
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break;
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}
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}
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if (ok) {
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ans.push(w);
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}
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}
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return ans;
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}

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