longest-common-subsequence.java

/*
Given two strings text1 and text2, return the length of their longest common subsequence. If there is no common subsequence, return 0.

A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.

For example, "ace" is a subsequence of "abcde".
A common subsequence of two strings is a subsequence that is common to both strings.

Input: text1 = "abcde", text2 = "ace" 
Output: 3  
Explanation: The longest common subsequence is "ace" and its length is 3.

Submission Links: https://leetcode.com/submissions/detail/806171350/

*/

class LongestCommonSubsequence {
    public int longestCommonSubsequence(String text1, String text2) {
        int dp[][] = new int[text1.length()+1][text2.length()+1];
        
        for(int[] a: dp){
            Arrays.fill(a, 0);
        }
        
        for(int i=1; i<=text1.length(); i++){
            for(int j=1; j<=text2.length(); j++){
                if(text1.charAt(i-1) == text2.charAt(j-1)){
                    dp[i][j] = 1 + dp[i-1][j-1];
                }
                else{
                    dp[i][j] = Math.max(dp[i][j-1], dp[i-1][j]);
                }
            }
        }
        
        StringBuilder sb = new StringBuilder();
        int i = text1.length();
        int j = text2.length();
        
        while(i>0 && j>0){
            if(text1.charAt(i-1) == text2.charAt(j-1)){
                sb.append(text1.charAt(i-1));
                i--;
                j--;
            }
            else if(dp[i-1][j] > dp[i][j-1]){
                i--;    
            }
            else{
                j--;
            }
            
        }
        sb.reverse();
        System.out.println(sb.toString());
        
        return dp[text1.length()][text2.length()];
    }
}