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Aug 13, 2023
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feat: add solutions to lc/lcof2 problems #1437

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248 changes: 154 additions & 94 deletions lcof2/剑指 Offer II 087. 复原 IP/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -64,7 +64,17 @@

<!-- 这里可写通用的实现逻辑 -->

DFS。
**方法一：DFS**

我们定义一个函数 $dfs(i)$，表示从字符串 $s$ 的第 $i$ 位开始，搜索能够组成的 IP 地址列表。

函数 $dfs(i)$ 的执行步骤如下：

如果 $i$ 大于等于字符串 $s$ 的长度，说明已经完成了四段 IP 地址的拼接，判断是否满足四段 IP 地址的要求，如果满足则将当前 $IP$ 加入答案。

如果 $i$ 小于字符串 $s$ 的长度，此时还需要拼接 $IP$ 地址的一段，此时需要确定这一段 $IP$ 地址的值。如果该值大于 $255$，或者当前位置 $i$ 为 $0$ 且 $i$ 之后的若干位的数值大于 $0$，则说明不满足要求，直接返回。否则，将其加入 $IP$ 地址列表，并继续搜索下一段 $IP$ 地址。

时间复杂度 $O(n \times 3^4)$，空间复杂度 $O(n)$。其中 $n$ 为字符串 $s$ 的长度。

<!-- tabs:start -->

Expand All @@ -75,26 +85,27 @@ DFS。
```python
class Solution:
def restoreIpAddresses(self, s: str) -> List[str]:
def check(s):
if not (0 <= int(s) <= 255):
return False
if s[0] == '0' and len(s) > 1:
def check(i: int, j: int) -> int:
if s[i] == "0" and i != j:
return False
return True
return 0 <= int(s[i : j + 1]) <= 255

def dfs(s, t):
if len(t) == 4:
if not s:
ans.append('.'.join(t))
def dfs(i: int):
if i >= n and len(t) == 4:
ans.append(".".join(t))
return
if i >= n or len(t) >= 4:
return
for i in range(1, min(4, len(s) + 1)):
if check(s[:i]):
t.append(s[:i])
dfs(s[i:], t)
for j in range(i, min(i + 3, n)):
if check(i, j):
t.append(s[i : j + 1])
dfs(j + 1)
t.pop()

n = len(s)
ans = []
dfs(s, [])
t = []
dfs(0)
return ans
```

Expand All @@ -104,43 +115,36 @@ class Solution:

```java
class Solution {
private List<String> ans;
private int n;
private String s;
private List<String> ans = new ArrayList<>();
private List<String> t = new ArrayList<>();

public List<String> restoreIpAddresses(String s) {
ans = new ArrayList<>();
dfs(s, new ArrayList<>());
n = s.length();
this.s = s;
dfs(0);
return ans;
}

private void dfs(String s, List<String> t) {
if (t.size() == 4) {
if ("".equals(s)) {
ans.add(String.join(".", t));
}
private void dfs(int i) {
if (i >= n && t.size() == 4) {
ans.add(String.join(".", t));
return;
}
for (int i = 1; i < Math.min(4, s.length() + 1); ++i) {
String c = s.substring(0, i);
if (check(c)) {
t.add(c);
dfs(s.substring(i), t);
t.remove(t.size() - 1);
}
}
}

private boolean check(String s) {
if ("".equals(s)) {
return false;
}
int num = Integer.parseInt(s);
if (num > 255) {
return false;
if (i >= n || t.size() >= 4) {
return;
}
if (s.charAt(0) == '0' && s.length() > 1) {
return false;
int x = 0;
for (int j = i; j < Math.min(i + 3, n); ++j) {
x = x * 10 + s.charAt(j) - '0';
if (x > 255 || (s.charAt(i) == '0' && i != j)) {
break;
}
t.add(s.substring(i, j + 1));
dfs(j + 1);
t.remove(t.size() - 1);
}
return true;
}
}
```
Expand All @@ -151,75 +155,131 @@ class Solution {
class Solution {
public:
vector<string> restoreIpAddresses(string s) {
int n = s.size();
vector<string> ans;
vector<string> t;
dfs(s, t, ans);
return ans;
}

void dfs(string s, vector<string>& t, vector<string>& ans) {
if (t.size() == 4) {
if (s == "") {
string p = "";
for (auto e : t) p += e + ".";
p.pop_back();
ans.push_back(p);
function<void(int)> dfs = [&](int i) {
if (i >= n && t.size() == 4) {
ans.push_back(t[0] + "." + t[1] + "." + t[2] + "." + t[3]);
return;
}
return;
}
for (int i = 1; i < min(4, (int) s.size() + 1); ++i) {
string c = s.substr(0, i);
if (check(c)) {
t.push_back(c);
dfs(s.substr(i, s.size() - i), t, ans);
if (i >= n || t.size() >= 4) {
return;
}
int x = 0;
for (int j = i; j < min(n, i + 3); ++j) {
x = x * 10 + s[j] - '0';
if (x > 255 || (j > i && s[i] == '0')) {
break;
}
t.push_back(s.substr(i, j - i + 1));
dfs(j + 1);
t.pop_back();
}
}
}

bool check(string s) {
if (s == "") return false;
int num = stoi(s);
if (num > 255) return false;
if (s[0] == '0' && s.size() > 1) return false;
return true;
};
dfs(0);
return ans;
}
};
```

### **Go**

```go
func restoreIpAddresses(s string) []string {
check := func(s string) bool {
if i, _ := strconv.Atoi(s); i > 255 {
return false
}
if s[0] == '0' && len(s) > 1 {
return false
func restoreIpAddresses(s string) (ans []string) {
n := len(s)
t := []string{}
var dfs func(int)
dfs = func(i int) {
if i >= n && len(t) == 4 {
ans = append(ans, strings.Join(t, "."))
return
}
return true
}
var ans []string
var dfs func(s string, t []string)
dfs = func(s string, t []string) {
if len(t) == 4 {
if s == "" {
ans = append(ans, strings.Join(t, "."))
}
if i >= n || len(t) == 4 {
return
}
for i := 1; i < 4 && i < len(s)+1; i++ {
if check(s[0:i]) {
t = append(t, s[0:i])
dfs(s[i:], t)
t = t[0 : len(t)-1]
x := 0
for j := i; j < i+3 && j < n; j++ {
x = x*10 + int(s[j]-'0')
if x > 255 || (j > i && s[i] == '0') {
break
}
t = append(t, s[i:j+1])
dfs(j + 1)
t = t[:len(t)-1]
}
}
var t []string
dfs(s, t)
return ans
dfs(0)
return
}
```

### **TypeScript**

```ts
function restoreIpAddresses(s: string): string[] {
const n = s.length;
const ans: string[] = [];
const t: string[] = [];
const dfs = (i: number): void => {
if (i >= n && t.length === 4) {
ans.push(t.join('.'));
return;
}
if (i >= n || t.length === 4) {
return;
}
let x = 0;
for (let j = i; j < i + 3 && j < n; ++j) {
x = x * 10 + s[j].charCodeAt(0) - '0'.charCodeAt(0);
if (x > 255 || (j > i && s[i] === '0')) {
break;
}
t.push(x.toString());
dfs(j + 1);
t.pop();
}
};
dfs(0);
return ans;
}
```

### **C#**

```cs
public class Solution {
private IList<string> ans = new List<string>();
private IList<string> t = new List<string>();
private int n;
private string s;

public IList<string> RestoreIpAddresses(string s) {
n = s.Length;
this.s = s;
dfs(0);
return ans;
}

private void dfs(int i) {
if (i >= n && t.Count == 4) {
ans.Add(string.Join(".", t));
return;
}
if (i >= n || t.Count == 4) {
return;
}
int x = 0;
for (int j = i; j < i + 3 && j < n; ++j) {
x = x * 10 + (s[j] - '0');
if (x > 255 || (j > i && s[i] == '0')) {
break;
}
t.Add(x.ToString());
dfs(j + 1);
t.RemoveAt(t.Count - 1);
}
}
}
```

Expand Down
64 changes: 28 additions & 36 deletions lcof2/剑指 Offer II 087. 复原 IP/Solution.cpp
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Original file line number Diff line number Diff line change
@@ -1,37 +1,29 @@
class Solution {
public:
vector<string> restoreIpAddresses(string s) {
vector<string> ans;
vector<string> t;
dfs(s, t, ans);
return ans;
}

void dfs(string s, vector<string>& t, vector<string>& ans) {
if (t.size() == 4) {
if (s == "") {
string p = "";
for (auto e : t) p += e + ".";
p.pop_back();
ans.push_back(p);
}
return;
}
for (int i = 1; i < min(4, (int) s.size() + 1); ++i) {
string c = s.substr(0, i);
if (check(c)) {
t.push_back(c);
dfs(s.substr(i, s.size() - i), t, ans);
t.pop_back();
}
}
}

bool check(string s) {
if (s == "") return false;
int num = stoi(s);
if (num > 255) return false;
if (s[0] == '0' && s.size() > 1) return false;
return true;
}
class Solution {
public:
vector<string> restoreIpAddresses(string s) {
int n = s.size();
vector<string> ans;
vector<string> t;
function<void(int)> dfs = [&](int i) {
if (i >= n && t.size() == 4) {
ans.push_back(t[0] + "." + t[1] + "." + t[2] + "." + t[3]);
return;
}
if (i >= n || t.size() >= 4) {
return;
}
int x = 0;
for (int j = i; j < min(n, i + 3); ++j) {
x = x * 10 + s[j] - '0';
if (x > 255 || (j > i && s[i] == '0')) {
break;
}
t.push_back(s.substr(i, j - i + 1));
dfs(j + 1);
t.pop_back();
}
};
dfs(0);
return ans;
}
};
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