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Solution.java
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Solution.java
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//
// DFS, Backtracking, String(Restore IP Addresses)
// https://leetcode.com/problems/restore-ip-addresses/
// Created by hyungwook on 2022/03/21.
//
import java.util.ArrayList;
import java.util.List;
import java.util.StringJoiner;
public class Solution {
List<String> answer = new ArrayList<>();
public List<String> restoreIpAddresses(String s) {
List<Integer> tmp = new ArrayList<>();
tmp.add(0);
dfs(s, tmp, 0, 0);
return answer;
}
private void dfs(String s, List<Integer> tmp, int dotNum, int l) {
if (dotNum == 3) {
tmp.add(s.length());
String ip = isValid(s, tmp);
tmp.remove(tmp.size() - 1);
if (ip != null) {
answer.add(ip);
}
return;
}
if (l == s.length() || dotNum > 3) {
return;
} else {
dfs(s, tmp, dotNum, l + 1);
tmp.add(l);
dfs(s, tmp, dotNum + 1, l + 1);
tmp.remove(tmp.size() - 1);
}
}
private String isValid(String s, List<Integer> tmp) {
for (int i = 0; i <= 3; i++) {
if (tmp.get(i + 1) - tmp.get(i) > 3) {
return null;
}
}
StringJoiner stringJoiner = new StringJoiner(".");
for (int i = 0; i <= 3; i++) {
String substring = s.substring(tmp.get(i), tmp.get(i + 1));
if ((substring.length() > 1 && substring.charAt(0) == '0') || substring.equals("")) {
return null;
}
Integer integer = Integer.valueOf(substring);
if (integer < 0 || integer > 255) {
return null;
} else {
stringJoiner.add(substring);
}
}
return stringJoiner.toString();
}
}