Leetcode: 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)

好多特殊情况：

递归到最后一个数是9245587303，stoi越界

多个零：10.000.0.1

数字前面是以0开始：10.010.0.1

 

vector<string> restore(string s, int n, bool &flag)

	{

		vector<string> res;

		if(s.length() < n) {flag = false; return res;}

		if(n==1)

		{

			if(s.length()>3){flag=false;return res;}//maybe larger than int

			int ip = stoi(s);

			if(ip==0 && s.length() >1) flag = false;

			else if(ip>0 && s[0] == '0') flag = false;

			else if((ip >= 0) && (ip < 256))

			{

				res.push_back(s);

				flag = true;

			}else

				flag = false;

			return res;

		}

		int loop = s.length() - n +1;//garuntee every ip address is no less than one bit

		loop = min(loop,3);

		for(int i = 1; i <= loop; i++)

		{

			string ipstr = s.substr(0,i);

			int ip = stoi(ipstr);

			if(ip==0 && ipstr.length() >1)break;

			if(ip>0 && ipstr[0] == '0')break;

			if((ip>=0) && (ip < 256))

			{

				string suffix = s.substr(i);

				bool f = false;

				vector<string> tmp = restore(suffix,n-1,f);

				if(f)

				{

					flag = true;

					for(int k = 0; k < tmp.size(); k++)

						res.push_back(ipstr + '.' + tmp[k]);

				}

			}

		}

		return res;

	}

	vector<string> restoreIpAddresses(string s) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

		vector<string> res;

		bool flag = false;

		res = restore(s,4,flag);

		return res;

    }