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"]

主要思想：採用递归的方式。一个一个的增加到最后的ip中

void formIpAddr(vector<string>&ret, string curIp, string nums, int idxIp){
if(idxIp==1){
if(nums.size()>3 || (nums.size()>1&&nums[0]=='0')){
return ;
}
const char * data=nums.c_str();
if(nums.size()<=2||atoi(data)<=255){
ret.push_back(curIp+nums);
return;
}
}
else{
if(nums[0]=='0'){
string tmp=curIp+nums.substr(0,1)+".";
formIpAddr(ret, tmp, nums.substr(1), idxIp-1);
return;
}
else{
int i;
string tmp;
for(i=0; i<2 && i+idxIp<=nums.size(); i++){
tmp=nums.substr(0, i+1);
formIpAddr(ret, curIp+tmp+".", nums.substr(i+1), idxIp-1);
}
if(i+idxIp<=nums.size()){
const char * data=nums.substr(0,i+1).c_str();
tmp=nums.substr(0, i+1);
if(atoi(data)<=255)
formIpAddr(ret, curIp+tmp+".", nums.substr(i+1), idxIp-1);
}
}
}

}

vector<string> restoreIpAddresses(string s) {
vector<string> ret;
if(s.size()<4)
return ret;
string curIp="";

formIpAddr(ret, curIp, s, 4);
return ret;
}