[JS] Longest Common Subsequence

🔒 문제 (LeetCode 1143)

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.

Constraints:

• 1 <= text1.length, text2.length <= 1000
• text1 and text2 consist of only lowercase English characters.

 

🌊 입출력

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.

 

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🔑 해결

🌌 알고리즘 - DP

/**
 * @param {string} text1
 * @param {string} text2
 * @return {number}
 */
var longestCommonSubsequence = function(text1, text2) {
    let m = text1.length
    let n = text2.length
    
    // dp[i][j] = text1[:i]와 text[:j]의 longest common subsequence
    let dp = new Array(m+1).fill().map(() => 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] = Math.max(dp[i-1][j], dp[i][j-1])
           } else {
                dp[i][j] = dp[i-1][j-1] + 1

           }
        }
    }
    
    return dp[m][n]
};