longest Common Prefix

一、问题描述

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: strs = ["flower","flow","flight"]
Output: "fl"

Example 2:

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

二、代码

思路：

1、选取字符串中的一个元素（第一个元素）为基准，遍历基准的字符，并与字符串中的其他元素的相应位置比较。时间复杂度为O(nlogm)。

2、按照字典序(ascii码)对字符串进行排序，然后寻找最大值和最小值的公共前缀。

C++：

class Solution {
public:
    string longestCommonPrefix(vector& strs) {
      if(strs.empty())
        {
            return "";
        }
    int length = strs[0].size();
    int count = strs.size();
    for (int i = 0; i < length ; i++)
    {
        char c = strs[0][i];
        for(int j = 1;j < count ;j++)
        {
            if(i == strs[j].size() || c != strs[j][i])
            {
                return strs[0].substr(0,i); //切割函数
            }
        }
    }
    return strs[0];
    }
};

python:

class Solution(object):
    def longestCommonPrefix(self, strs):
        """
        :type strs: List[str]
        :rtype: str
        """
        if not strs: return ""
        s1 = min(strs)
        s2 = max(strs)
        for i,x in enumerate(s1):
            if x != s2[i]:
                return s2[:i]
        return s1