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)

典型的深搜问题：

#include <iostream>
#include<vector>
#include <string>
using namespace std;


bool isValid(string s, int start, int end)
{
	if (s[start]=='0') //不能以0开头
	{
		return false;
	}
	if (end-start>3)   //防止num超出int范围溢出
	{
		return false;
	}

	
	int num = 0;
	for (int i=start;i<=end;i++)
	{
		num = num*10 + s[i]-'0';
	}

	if (num<=255)     //判断数字是否有效
	{
		return true;
	}
	
	return false;

}


void DFS(string s, int curPos, int curStep, string& curIP, vector<string>& result)
{
	if (s.size()-curPos > (5-curStep)*3)   //防止出现多于四个字段的情况 如：2.5.5.2.2.5
	{
		return;
	}
	
	if (curPos == s.size())
	{
		curIP.erase(curIP.end()-1);  //把最后一个字段多加的‘.’弹出
		result.push_back(curIP);
		return ;
	}

	for (int i=curPos;i<s.size();++i)
	{
		if (isValid(s,curPos,i))
		{
			curIP.insert(curIP.begin()+i+curStep, '.'); //压栈
			DFS(s,i+1,curStep+1,curIP,result);
			curIP.erase(curIP.begin()+i+curStep);       //出栈
		}
	}
}

int main()
{
	string s="25525511035";
	string curIP =s;
	vector<string> result;

	DFS(s,0,1,curIP,result);

	return 0;
}