题目连接:Leetcode 093 Restore IP Addresses
解题思路:DFS搜索,最多4层,每层的数不能超过255,不能有前缀0,到第4层时字符全用完时,为合法IP。
class Solution { public: void dfs(int d, int p, string s, string c, vector<string>& ans) { if (d == 4) { if (p == s.size()) ans.push_back(c.substr(0, c.size()-1)); return; } int n = s[p] - '0'; c = c + s[p++]; dfs(d + 1, p, s, c + ".", ans); if (n == 0) return; while (p < s.size()) { n = n * 10 + s[p] - '0'; if (n >= 0 && n <= 255) { c = c + s[p++]; dfs(d + 1, p, s, c + ".", ans); } else break; } } vector<string> restoreIpAddresses(string s) { vector<string> ans; dfs(0, 0, s, "", ans); return ans; } };