1143. Longest Common Subsequence

Given two strings text1 and text2, return the length of their longest common subsequence.

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. (eg, "ace" is a subsequence of "abcde" while "aec" is not). A common subsequence of two strings is a subsequence that is common to both strings.

If there is no common subsequence, return 0.

Example 1:

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

Example 2:

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

Example 3:

Input: text1 = "abc", text2 = "def"
Output: 0
Explanation: There is no such common subsequence, so the result is 0.

Constraints:

• 1 <= text1.length <= 1000
• 1 <= text2.length <= 1000
• The input strings consist of lowercase English characters only.

class Solution {
    public int longestCommonSubsequence(String text1, String text2) {
        int res = 0;
        int l1 = text1.length();
        int l2 = text2.length();
        int[][] dp = new int[l1+1][l2+1];
        
        for(int i = 1; i <= l1; i++){
            for(int j = 1; j <= l2; 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-1][j], dp[i][j-1]);
                }
            }
        }
        return dp[l1][l2];
    }
}