LeetCode:Restore IP Addresses

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Restore IP Addresses

Total Accepted: 57183 Total Submissions: 241109 Difficulty: 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)

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Backtracking String

思路：

将字符串分成4份（使用3个指针），当4部分都合法时才valid。

c++ code:

class Solution {public:    vector<string> restoreIpAddresses(string s) {                vector<string> ret;        int len = s.size();                for(int i=1;i<4 && i<len-2;i++) { //第1个分隔点            for(int j=i+1;j<i+4 && j<len-1;j++) { //第2个分隔点                for(int k=j+1;k<j+4 && k<len;k++) { //第3个分隔点                    string s1 = s.substr(0,i);                    string s2 = s.substr(i,j-i);                    string s3 = s.substr(j,k-j);                    string s4 = s.substr(k);                    if(isLegal(s1) && isLegal(s2) && isLegal(s3) && isLegal(s4)) {                        ret.push_back(s1+"."+s2+"."+s3+"."+s4);                    }                }            }        }        return ret;    }        // 自定义函数    bool isLegal(string s) {        if(s.size()>3 || s.size()==0 || (s.size()>1 && s[0]=='0') || atoi(s.c_str())>255)            return false;        return true;    }};

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