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author ： Power button (LeetCode)
link ：https://leetcode-cn.com/leetbook/read/top-interview-questions-easy/xnmav1/
source ： Power button （LeetCode）
The copyright belongs to the author . Commercial reprint please contact the author for authorization , Non-commercial reprint please indicate the source .

Topic 1 ： The longest common prefix

Write a function to find the longest common prefix in the string array .
If no common prefix exists , Returns an empty string “”.

Example 1：
Input ：strs = [“flower”,“flow”,“flight”]
Output ：“fl”

Example 2：
Input ：strs = [“dog”,“racecar”,“car”]
Output ：""
explain ： Input does not have a common prefix .

Tips ：
1 <= strs.length <= 200
0 <= strs[i].length <= 200
strs[i] It's only made up of lowercase letters

Related labels
character string

C++ Source program ：

class Solution {
    
public:
    string longestCommonPrefix(vector<string>& strs) {
    
        //  I don't know why I use length()  Compilation error 
        //  First judge strs When the array does not exist 
        if (strs.size() == 0)
            return "";

        //  Assume that the first string of the array is the public prefix of the second .
        string pre = strs[0];
        int i = 1;  //  At least two arrays , If only one , Then it itself is the longest public prefix , So from 1 Start 
        while(i < strs.size()){
    
            while(strs[i].find(pre) != 0)  //  From the second string of the array （ Subscript to be 1） Start ,find The function looks for the existence of the first （ That is, the previous string ） The characters of . If there is , Will return the address of the first character , Return 0 It means that the first and second have the same common prefix 
                pre = pre.substr(0, pre.size() - 1 );// substr Intercept pre from 0 Subscript to length -1  The number of   character . For example size() = 4,  that substr(0,4-1), That is, intercept the subscript 0 Start length is 3 String , Subscript to be 0,1,2  This string of .
            i++;
        }
        return pre;
    }
};

Personal experience ：

Read this question , A key factor must be understood —— That is, the prefix in the longest common prefix , That is, it can only be the prefix composed of the first few characters in each string . Make this point , Then you can know that what you have to consider is not very responsible .
We can directly assume that the first string of the array is the longest common prefix , And find out the longest common prefix between it and the second string . If there isn't the same , So long back “”, non-existent .

Related to knowledge ：

1. str1.find(str2) function
   I.e. find str1 in str2 The first subscript address of the string

I am CSDN Blog has detailed knowledge explanation ：
https://blog.csdn.net/D16100/article/details/121978209?spm=1001.2014.3001.5501

2. str1.substr(a,b) function
   Intercepting string str1 In the from a At the beginning b A string of length

I am CSDN Blog has detailed knowledge explanation ：
https://blog.csdn.net/D16100/article/details/121978625