题解 | #数字字符串转化成IP地址#
数字字符串转化成IP地址
https://www.nowcoder.com/practice/ce73540d47374dbe85b3125f57727e1e
import java.util.*;
public class Solution {
private List<List<String>> ipList = new ArrayList<>();
/**
*
* @param s string字符串
* @return string字符串ArrayList
*/
public ArrayList<String> restoreIpAddresses (String s) {
// write code here
if (s == null || s.length() < 1) {
return new ArrayList<>();
}
dfs(s, 0, new ArrayList<>());
ArrayList<String> res = new ArrayList<>();
for (List<String> list : ipList) {
res.add(list2Ip(list));
}
return res;
}
private void dfs(String str, int start, List<String> list) {
int n = str.length();
if (start == n && list.size() == 4) {
ipList.add(new ArrayList<>(list));
return;
}
for (int i = start; i < n; i++) {
if (i - start >= 1 && str.charAt(start) == '0') {
break;
}
if (Integer.parseInt(str.substring(start, i + 1)) > 255) {
break;
}
list.add(str.substring(start, i + 1));
dfs(str, i + 1, list);
list.remove(list.size() - 1);
}
}
private String list2Ip(List<String> list) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 3; i++) {
sb.append(list.get(i)).append(".");
}
sb.append(list.get(3));
return sb.toString();
}
}
