Leetcode 93. Restore IP Addresses (Medium) (cpp)

Niko_Ke

于 2016-08-22 11:06:57 发布

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本文解析了LeetCode上的第93题——恢复IP地址，并提供了中等难度的回溯法C++实现方案。介绍了如何从一个仅包含数字的字符串中恢复所有可能的有效IP地址组合。

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Leetcode 93. Restore IP Addresses (Medium) (cpp)

Tag: Backtracking, String

Difficulty: Medium

/*

93. Restore IP Addresses (Medium)

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) {
		vector<string> res;
		if (s.length() < 4 || s.length() > 12) return res;
		generate(s, 0, 4, res, "");
		return res;
	}
	void generate(string s, int start, int cnt, vector<string>& res, string res_sub) {
		if (start == s.length() && cnt == 0) {
			res_sub.pop_back();
			res.push_back(res_sub);
			return;
		}
		if(s.length() - start > 3 * cnt) return;
		for (int i = 0; i + start < s.length() && i < 3; i++) {
			if (i == 0) generate(s, start + 1, cnt - 1, res, res_sub + s.substr(start, 1) + ".");
			if (i == 1 && s[start] != '0') generate(s, start + 2, cnt - 1, res, res_sub + s.substr(start, 2) + ".");
			if (i == 2 && stoi(s.substr(start, 3)) > 99 && stoi(s.substr(start, 3)) < 256) generate(s, start + 3, cnt - 1, res, res_sub + s.substr(start, 3) + ".");
		}
	}
};