leetcode刷题计划Day13

文章目录

• • • 93. 复原 IP 地址【中等】

93. 复原 IP 地址【中等】

https://leetcode-cn.com/problems/restore-ip-addresses/

public class Solution {

    public List<String> restoreIpAddresses(String s) {
        int len = s.length();
        List<String> res = new ArrayList<>();
        if (len > 12 || len < 4) {
            return res;
        }

        Deque<String> path = new ArrayDeque<>(4);
        dfs(s, len, 0, 4, path, res);
        return res;
    }

    // 需要一个变量记录剩余多少段还没被分割
    private void dfs(String s, int len, int begin, int residue, Deque<String> path, List<String> res) {
        if (begin == len) {
            if (residue == 0) {
                res.add(String.join(".", path));
            }
            return;
        }

        for (int i = begin; i < begin + 3; i++) {
            if (i >= len) {
                break;
            }

            if (residue * 3 < len - i) {
                continue;
            }

            if (judgeIpSegment(s, begin, i)) {
                String currentIpSegment = s.substring(begin, i + 1);
                path.addLast(currentIpSegment);

                dfs(s, len, i + 1, residue - 1, path, res);
                path.removeLast();
            }
        }
    }

    private boolean judgeIpSegment(String s, int left, int right) {
        int len = right - left + 1;
        if (len > 1 && s.charAt(left) == '0') {
            return false;
        }

        int res = 0;
        while (left <= right) {
            res = res * 10 + s.charAt(left) - '0';
            left++;
        }

        return res >= 0 && res <= 255;
    }
}