LeetCode Restore IP Addresses-优快云博客

本文介绍了一种通过深度优先搜索实现的算法，该算法能够将一个仅由数字组成的字符串恢复成所有可能的有效IP地址组合。例如，对于输入25525511135，可以得到[255.255.11.135255.255.111.35]等有效IP地址。

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题目：

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

For example:
Given "25525511135",

return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)

class Solution {
public:
	vector<string> restoreIpAddresses(string s) {
		dfs(0, 4, s, 0);
		return ans;
	}
private:
	int pos[4];
	vector<string> ans;
	//判断ip地址是否符合要求
	bool isValid(string s, int beg, int end) {
		string ip(s, beg, end - beg + 1);
		if (ip.size() == 1)
		    return "0" <= ip && ip <="9";
		else if(ip.size() == 2)
			return "10" <= ip && ip <= "99";
		else if (ip.size() == 3)
			return  "100" <= ip && ip <= "255";
		return false;
	}
	//深度搜索
	void dfs(int depth, int maxDepth, string &s, int start) {
		if (depth == maxDepth) {
			if (start == s.size()) {
				string addr;
				int beg = 0;
				for (int i = 0; i < 4; i++) {
					string ip(s, beg, pos[i] - beg + 1);
					beg = pos[i] + 1;
					addr += i == 0 ? ip : "." + ip;
				}
				ans.push_back(addr);
			}
			return;
		}
		for (int i = start; i < s.size(); i++) {
			if (isValid(s, start, i)) {
				pos[depth] = i;
				dfs(depth + 1, maxDepth, s, i + 1);
			}
		}
	}
};