LeetCode Restore IP Addresses

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)

class Solution {
public:
    vector<string> restoreIpAddresses(string s) {
    	const char* str = s.c_str();
		vector<string> ret;
		int size = s.size();
		for(int i = 1; i < size; ++i)
		{
			if(!isValid(str, i))
				continue;
			for(int j = i+1; j < size; ++j)
			{
				if(!isValid(str+i, j-i))
					continue;
				for(int k = j+1; k < size; ++k)
				{
					if(!isValid(str+j, k-j))
						continue;
					if(isValid(str+k, size-k))
					{
						ret.push_back(s.substr(0, i) + "." + s.substr(i, j-i) + 
							"." + s.substr(j, k-j) + "." + s.substr(k, size-k));
					}
				}
			}
		}
		return ret;
    }
	bool isValid(const char* s, int len)
	{
		if('0' == s[0])
			if(1 == len)
				return true;
			else
				return false;
		int temp = 0;
		for(int i = 0; i < len; ++i)
		{
			temp = temp*10 + (int)(s[i] - '0');
			if(temp > 255)
				return false;
		}
		if(temp <= 255 && temp >= 1)
			return true;
		else
			return false;
	}
};