14. Longest Common Prefix(Solution || Leetcode easy || Java)

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.

Constraints:

• 1 <= strs.length <= 200
• 0 <= strs[i].length <= 200
• strs[i] consists of only lowercase English letters.

SOLUTION(1):

Non-optimized

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if(strs[0].equals("")){
            return "";
        }
        
        String prefix = strs[0];
        
        for(int i = 1; i < strs.length; i++){

       if(strs[i].equals("") || strs[i].charAt(0) != prefix.charAt(0)){
           return "";
         }

            if(strs[i].length() < prefix.length()){

                boolean temp = true;
                
                for(int j = 0; j < strs[i].length(); j++){
                    if(strs[i].charAt(j) != prefix.charAt(j)){
                        prefix = prefix.substring(0,j);
                        temp = false;
                        break;
                    }
                }
                if(temp){
                    prefix = strs[i];
                }
            }
            else{
                for(int j = 0; j < prefix.length(); j++){
                    if(strs[i].charAt(j) != prefix.charAt(j)){
                        prefix = prefix.substring(0,j);
                        break;
                    }
                }
            }
        }
        
        return prefix;
    }
}

SOLUTION(2):

Optimized

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if(strs[0].equals("")){
            return "";
        }
        
        String prefix = strs[0];
        
        for(int i = 1; i < strs.length; i++){
            
//if we do not find prefix at the starting of the string then we 
//are going to decrease the size of prefix
            while(strs[i].indexOf(prefix) != 0){
                prefix = prefix.substring(0,prefix.length() -1);
            }
        }
        
        return prefix;
    }
}

Runtime: 0 ms, faster than 100.00% of Java online submissions for Longest Common Prefix.

Memory Usage: 40.4 MB, less than 89.19% of Java online submissions for Longest Common Prefix.

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