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feat: add solutions to lc problems: No.1903,1904,1905,1906
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‎solution/1900-1999/1903.Largest Odd Number in String/README.md

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# [1903. 字符串中的最大奇数](https://leetcode-cn.com/problems/largest-odd-number-in-string)
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[English Version](/solution/1900-1999/1903.Largest%20Odd%20Number%20in%20String/README_EN.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>给你一个字符串 <code>num</code> ，表示一个大整数。请你在字符串 <code>num</code> 的所有 <strong>非空子字符串</strong> 中找出 <strong>值最大的奇数</strong> ，并以字符串形式返回。如果不存在奇数，则返回一个空字符串<em> </em><code>""</code><em> </em>。</p>
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<p><strong>子字符串</strong> 是字符串中的一个连续的字符序列。</p>
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<p> </p>
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<p><strong>示例 1：</strong></p>
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<pre>
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<strong>输入：</strong>num = "52"
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<strong>输出：</strong>"5"
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<strong>解释：</strong>非空子字符串仅有 "5"、"2" 和 "52" 。"5" 是其中唯一的奇数。
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</pre>
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<p><strong>示例 2：</strong></p>
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<pre>
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<strong>输入：</strong>num = "4206"
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<strong>输出：</strong>""
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<strong>解释：</strong>在 "4206" 中不存在奇数。
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</pre>
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<p><strong>示例 3：</strong></p>
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<pre>
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<strong>输入：</strong>num = "35427"
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<strong>输出：</strong>"35427"
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<strong>解释：</strong>"35427" 本身就是一个奇数。
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</pre>
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<p> </p>
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<p><strong>提示：</strong></p>
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<ul>
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<li><code>1 <= num.length <= 10<sup>5</sup></code></li>
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<li><code>num</code> 仅由数字组成且不含前导零</li>
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</ul>
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## 解法
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<!-- 这里可写通用的实现逻辑 -->
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从后往前遍历字符串中的每个数字，遇到奇数则直接返回结果。若遍历结束仍未遇到奇数，返回空字符串。
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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 largestOddNumber(self, num: str) -> str:
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for i in range(len(num) - 1, -1, -1):
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if (int(num[i]) & 1) == 1:
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return num[:i + 1]
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return ''
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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 String largestOddNumber(String num) {
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for (int i = num.length() - 1; i >= 0; --i) {
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int c = num.charAt(i) - '0';
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if ((c & 1) == 1) {
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return num.substring(0, i + 1);
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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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```
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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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string largestOddNumber(string num) {
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for (int i = num.size() - 1; i >= 0; --i) {
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int c = num[i] - '0';
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if ((c & 1) == 1) {
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return num.substr(0, i + 1);
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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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```
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### **Go**
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```go
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func largestOddNumber(num string) string {
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for i := len(num) - 1; i >= 0; i-- {
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c := num[i] - '0'
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if (c & 1) == 1 {
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return num[:i+1]
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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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### **...**
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```
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```
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<!-- tabs:end -->

‎solution/1900-1999/1903.Largest Odd Number in String/README_EN.md

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# [1903. Largest Odd Number in String](https://leetcode.com/problems/largest-odd-number-in-string)
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[中文文档](/solution/1900-1999/1903.Largest%20Odd%20Number%20in%20String/README.md)
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## Description
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<p>You are given a string <code>num</code>, representing a large integer. Return <em>the <strong>largest-valued odd</strong> integer (as a string) that is a <strong>non-empty substring</strong> of </em><code>num</code><em>, or an empty string </em><code>&quot;&quot;</code><em> if no odd integer exists</em>.</p>
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<p>A <strong>substring</strong> is a contiguous sequence of characters within a string.</p>
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<p>&nbsp;</p>
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<p><strong>Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> num = &quot;52&quot;
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<strong>Output:</strong> &quot;5&quot;
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<strong>Explanation:</strong> The only non-empty substrings are &quot;5&quot;, &quot;2&quot;, and &quot;52&quot;. &quot;5&quot; is the only odd number.
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</pre>
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<p><strong>Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> num = &quot;4206&quot;
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<strong>Output:</strong> &quot;&quot;
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<strong>Explanation:</strong> There are no odd numbers in &quot;4206&quot;.
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</pre>
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<p><strong>Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> num = &quot;35427&quot;
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<strong>Output:</strong> &quot;35427&quot;
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<strong>Explanation:</strong> &quot;35427&quot; is already an odd number.
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 &lt;= num.length &lt;= 10<sup>5</sup></code></li>
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<li><code>num</code> only consists of digits and does not contain any leading zeros.</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 largestOddNumber(self, num: str) -> str:
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for i in range(len(num) - 1, -1, -1):
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if (int(num[i]) & 1) == 1:
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return num[:i + 1]
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return ''
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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 String largestOddNumber(String num) {
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for (int i = num.length() - 1; i >= 0; --i) {
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int c = num.charAt(i) - '0';
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if ((c & 1) == 1) {
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return num.substring(0, i + 1);
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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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```
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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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string largestOddNumber(string num) {
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for (int i = num.size() - 1; i >= 0; --i) {
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int c = num[i] - '0';
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if ((c & 1) == 1) {
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return num.substr(0, i + 1);
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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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```
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### **Go**
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```go
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func largestOddNumber(num string) string {
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for i := len(num) - 1; i >= 0; i-- {
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c := num[i] - '0'
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if (c & 1) == 1 {
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return num[:i+1]
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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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### **...**
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```
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```
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<!-- tabs:end -->

‎solution/1900-1999/1903.Largest Odd Number in String/Solution.cpp

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class Solution {
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public:
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string largestOddNumber(string num) {
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for (int i = num.size() - 1; i >= 0; --i) {
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int c = num[i] - '0';
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if ((c & 1) == 1) {
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return num.substr(0, i + 1);
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}
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}
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return "";
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}
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};

‎solution/1900-1999/1903.Largest Odd Number in String/Solution.go

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func largestOddNumber(num string) string {
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for i := len(num) - 1; i >= 0; i-- {
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c := num[i] - '0'
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if (c & 1) == 1 {
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return num[:i+1]
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}
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}
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return ""
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}

‎solution/1900-1999/1903.Largest Odd Number in String/Solution.java

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class Solution {
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public String largestOddNumber(String num) {
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for (int i = num.length() - 1; i >= 0; --i) {
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int c = num.charAt(i) - '0';
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if ((c & 1) == 1) {
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return num.substring(0, i + 1);
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}
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}
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return "";
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}
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}

‎solution/1900-1999/1903.Largest Odd Number in String/Solution.py

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class Solution:
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def largestOddNumber(self, num: str) -> str:
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for i in range(len(num) - 1, -1, -1):
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if (int(num[i]) & 1) == 1:
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return num[:i + 1]
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return ''

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