題目描述

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: ["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.

解題思路

思路一：

To employ this idea, the algorithm iterates through the strings [S1…Sn][S_1 \ldots S_n][S1​…Sn​], finding at each iteration iii the longest common prefix of strings LCP(S1…Si)LCP(S_1 \ldots S_i)LCP(S1​…Si​) When LCP(S1…Si)LCP(S_1 \ldots S_i)LCP(S1​…Si​) is an empty string, the algorithm ends. Otherwise after nnn iterations, the algorithm returns LCP(S1…Sn)LCP(S_1 \ldots S_n)LCP(S1​…Sn​)

程式碼如下

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if(strs.length==0 || strs == null){
            return "";
        }
        String prefix = strs[0];
        for(int i=1;i<strs.length;i++){
            while(strs[i].indexOf(prefix) != 0){
                prefix = prefix.substring(0,prefix.length()-1);
                if(prefix.isEmpty()){
                    return "";
                }
            }
        }
        return prefix;
    }
}
 

知識點總結

String 類中的方法indexOf(String s )：當字串s是呼叫該方法的字串的子串時返回0，否則返回-1