Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string "".

Example 1:

Input: ["flower","flow","flight"]
Output: "fl"

Example 2:

Input: ["dog","racecar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

題目翻譯：

一個vector<string> vec裡邊存了很多string，求這些string的最大相同的頭部分。

很簡單的題目，從頭依次遍歷即可，如果vec是空的，返回空，如果vec是1，則直接把結果返回，如果vec>=2，繼續查詢公共最大的範圍。

#include<iostream>
#include<cmath>
#include<string>
#include<vector>


using namespace std;


class Solution{
public:
	string longestCommonPrefix(vector<string> &vec)
	{
		string str="";
		int n=vec.size();
		if(n==0)
			return str;
		if(n==1)
		{
			str=vec[0];
			return str;
		}

		int count=0;
		int istrue=0;


		int max=vec[0].length();
		while(count<max)
		{		
			char temp=vec[0][count];
			for(int i=1;i<n;i++)
			{
				if(temp!=vec[i][count])
					istrue=1;

			}
			if(istrue==1)
				break;
			else
				count++;
		}
		for(int i=0;i<count;i++)
			str+=vec[0][i];

		return str;
	
	}
};



int main()
{   
	vector<string> vec;
	vec.push_back("flower");
	vec.push_back("flow");
	vec.push_back("flight");

	Solution so;
	string str=so.longestCommonPrefix(vec);
	cout<<str<<endl;




	system("pause");
	return 0;
}