longestCommonSubsequence.js

/*
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.

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

Example 3:
Input: text1 = "abc", text2 = "def"
Output: 0

Constraints:
    1 <= text1.length, text2.length <= 1000
    text1 and text2 consist of only lowercase English characters.
*/

/**
 * @param {string} text1
 * @param {string} text2
 * @return {number}
 */
function longestCommonSubsequence(text1, text2) {
    const m = text1.length, n = text2.length;
    const dp = Array.from({ length: m + 1 }, () => new Array(n + 1).fill(0));

    for (let i = 1; i <= m; i++) {
        for (let j = 1; j <= n; j++) {
            if (text1[i - 1] === text2[j - 1]) {
                dp[i][j] = dp[i - 1][j - 1] + 1;
            } else {
                dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
            }
        }
    }
    return dp[m][n];
}

// Example usage:
console.log(longestCommonSubsequence("abcde", "ace")); // Output: 3
console.log(longestCommonSubsequence("abc", "def"));   // Output: 0