LeetCode-in-All

1143. Longest Common Subsequence

Medium

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.

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:

Solution

class Solution {
    func longestCommonSubsequence(_ text1: String, _ text2: String) -> Int {
        let text1 = Array(text1), text2 = Array(text2)
        let n = text1.count 
        let m = text2.count
        var dp = [Int](repeating: 0, count: m + 1)
        for i in 0..<n {
            var curRow = [Int](repeating: 0, count: m + 1)
            for j in 0..<m {
                if text1[i] == text2[j] {
                    curRow[j + 1] = 1 + dp[j]
                } else {
                    curRow[j + 1] = max(dp[j + 1], curRow[j])
                }
            }
            dp = curRow
        }
        return dp[m]
    }
}