1143. Longest Common Subsequence

1. 문제

1-1. 원문

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.

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

1-2. 내용 번역

최장 공통 부분 수열을 구하여라.

2. 문제 이해

LCS 문제 날것 그 자체이다. (LCS Algorithm 참고)

3. 구현

class Solution {
    fun longestCommonSubsequence(text1: String, text2: String): Int {
        val text1Length = text1.length
        val text2Length = text2.length
        val lcsArr: Array<IntArray> = Array(text1Length+1){IntArray(text2Length+1){0}}

        text1.forEachIndexed { text1Idx, text1Char ->
            text2.forEachIndexed { text2Idx, text2Char ->
                lcsArr[text1Idx+1][text2Idx+1] = if (text1Char == text2Char) {
                    lcsArr[text1Idx][text2Idx] + 1
                } else {
                    Math.max(lcsArr[text1Idx+1][text2Idx], lcsArr[text1Idx][text2Idx+1])
                }
            }
        }

        return lcsArr[text1Length][text2Length]
    }
}