java [14。最长的共同前缀] #Array #Leetcode #Easy

Posted 2021-05-08

public class Solution {
    /*
    *
    * 14. Longest Common Prefix
    * Write a function to find the longest common prefix string amongst an array of strings.
    * My stupid solution with O(n^2) Complexity.
    *
    * */

    public  String longestCommonPrefix(String[] strs) {

        if(strs == null || strs.length == 0)
            return "";
        String start = strs[0];
        for(int i = 1; i <= start.length(); i++){
            for(String s: strs){
                if(s.length() < i || !s.substring(0,i).equals(start.substring(0,i))){
                    return start.substring(0,i-1);
                }
            }
        }
        return start;
    }
}

    /*
    *  method 2:
    *  want the longest 
    *  choose the first string  in the array
    *  and shrink it until to the end
    * */
    public static String longestCommonPrefix2(String[] strs) {
        // corner case
        if(strs == null || strs.length == 0)
            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 == "")
                    return "";
            }
        }
        return prefix;
    }