A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.
- For example,
"0.1.2.201"and"192.168.1.1"are valid IP addresses, but"0.011.255.245","192.168.1.312"and"[email protected]"are invalid IP addresses.
Given a string s containing only digits, return all possible valid IP addresses that can be formed by inserting dots into s. You are not allowed to reorder or remove any digits in s. You may return the valid IP addresses in any order.
Example 1:
Input: s = "25525511135" Output: ["255.255.11.135","255.255.111.35"]
Example 2:
Input: s = "0000" Output: ["0.0.0.0"]
Example 3:
Input: s = "101023" Output: ["1.0.10.23","1.0.102.3","10.1.0.23","10.10.2.3","101.0.2.3"]
Constraints:
1 <= s.length <= 20sconsists of digits only.
DFS.
class Solution:
def restoreIpAddresses(self, s: str) -> List[str]:
def check(i: int, j: int) -> int:
if s[i] == "0" and i != j:
return False
return 0 <= int(s[i : j + 1]) <= 255
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 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 = []
t = []
dfs(0)
return ansclass Solution {
private int n;
private String s;
private List<String> ans = new ArrayList<>();
private List<String> t = new ArrayList<>();
public List<String> restoreIpAddresses(String s) {
n = s.length();
this.s = s;
dfs(0);
return ans;
}
private void dfs(int i) {
if (i >= n && t.size() == 4) {
ans.add(String.join(".", t));
return;
}
if (i >= n || t.size() >= 4) {
return;
}
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);
}
}
}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;
}
};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
}
if i >= n || len(t) == 4 {
return
}
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]
}
}
dfs(0)
return
}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;
}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);
}
}
}