1 題目要求：

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.

Note:

All given inputs are in lowercase letters a-z.

2 解決方法:

class Solution {
public:
	string longestCommonPrefix(vector<string>& strs) {
		if (strs.size() == 0) return "";
		string ret;
		for (int i = 0;i<strs[0].length(); i++) {
			for (int j = 1;j<strs.size(); j++) {
				if ((strs[j].length()<=i)||(strs[j][i]!=strs[0][i]))  return ret;
			}
			ret.push_back(strs[0][i]);
		}
		return ret;
	}
};
 

時間複雜度O(mn) 

空間複雜度O(1)