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

#include <vector>
#include <string>
#include <algorithm>

class Solution {
public:
    int longestCommonSubsequence(const std::string& text1, const std::string& text2) {
        int n = text1.size();
        int m = text2.size();
        std::vector<std::vector<int>> dp(n + 1, std::vector<int>(m + 1, 0));
        
        for (int i = 1; i <= n; ++i) {
            for (int j = 1; j <= m; ++j) {
                if (text1[i - 1] == text2[j - 1]) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                } else {
                    dp[i][j] = std::max(dp[i - 1][j], dp[i][j - 1]);
                }
            }
        }
        
        return dp[n][m];
    }
};