LeetCode:Restore IP Address

93. Restore IP Addresses

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)

Tags: Backtracking String

输入一个字符串，要求输出该字符串可能拆分成的ip地址形式。

思路：ipv4的地址应该是4段，每段0-255中的一个数。所以考虑4层DFS加一些剪枝条件即可。剪枝条件有：1、取3个字符串stoi作为地址时大于255；2、2位数或者3位数地址段以0开头

另外要检查第四段ip地址为0的情况，防止类似于"0000000"atoi之后也算作0的情况。

 class Solution {
 public:

     bool dfs(string input, int number, string ipAddress, vector<string> &result){
         if(input.length() == ){
             return false;
         }
         if(number == ){
             int addressNumber = stoi(input);
             if(input[] == ''){
                 if(!(input.length() ==  && addressNumber == ))
                     return false;
             }
             if(addressNumber <= ){
                 ipAddress = ipAddress + input;
                 result.push_back(ipAddress);
                 return true;
             }else{
                 return false;
             }
         }else{
             if(input.length() >= ){
                 dfs(input.substr(), number + , ipAddress + input.substr(, ) + ".", result);
             }
             if(input.length() >=  && input[] != ''){
                 dfs(input.substr(), number + , ipAddress + input.substr(, ) + ".", result);
             }
             if(input.length() >=  && input[] != ''){
                 int addressNumber = stoi(input.substr(, ));
                 if(addressNumber <= ){
                     dfs(input.substr(), number + , ipAddress + input.substr(, ) + ".", result);
                 }
             }
         }
         return true;
     }

     vector<string> restoreIpAddresses(string s) {
         vector<string> result;
         if(s.length() ==  || s.length() > ){
             return result;
         }
         string temp = "";
         dfs(s, , temp, result);
         return result;
     }
 };