[leetcode] Restore IP Addresses

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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)

最简单的情况，遍历……

class Solution {public:    vector<string> restoreIpAddresses(string s) {// Start typing your C/C++ solution below// DO NOT write int main() functionvector<string> ret;if(s.size()>12)return ret;int length=s.size();for(int i=1 ; i<4 ; i++)for(int j=1 ; j<4 ; j++)for(int k=1 ; k<4 ; k++)for(int l=1 ; l<4 ; l++){if(i+j+k+l!=length)continue;string s1,s2,s3,s4;s1.append(s.begin(),s.begin()+i);s2.append(s.begin()+i,s.begin()+i+j);s3.append(s.begin()+i+j,s.begin()+i+j+k);s4.append(s.begin()+i+k+j,s.end());if(check(s1)&&check(s2)&&check(s3)&&check(s4)){string s=s1+"."+s2+"."+s3+"."+s4;ret.push_back(s);}}return ret;}bool check(const string& s){if(s=="")return false;int n=s.size();        if(n>1 && s[0]=='0')            return false;int num=0;for(int i=0 ; i<n ; i++){num=num*10+(s[i]-'0');}if(num>255)return false;return true;}};