1143. Longest Common Subsequence

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1143. Longest Common Subsequence

Description

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:

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Input: text1 = "abcde", text2 = "ace"
Output: 3
Explanation: The longest common subsequence is "ace" and its length is 3.

Example 2:

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Input: text1 = "abc", text2 = "abc"
Output: 3
Explanation: The longest common subsequence is "abc" and its length is 3.

Example 3:

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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.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    string text1_;
    string text2_;
    vector<vector<int>> dp;

    int longestCommonSubsequence(string text1, string text2) {
        text1_ = text1;
        text2_ = text2;
        int m = text1.size(), n = text2.size();
        dp.resize(m, vector<int>(n, -1));
        int res = traverse(0, 0);
        return res;
    }

    int traverse(int i, int j) {
        if (i == text1_.size() || j == text2_.size()) {
            return 0;
        }
        if (dp[i][j] != -1) {
            return dp[i][j];
        }
        int res = 0;
        if (text1_[i] == text2_[j]) {
            res = 1 + traverse(i + 1, j + 1);
        } else {
            res = max(traverse(i, j + 1), traverse(i + 1, j));
        }
        dp[i][j] = res;
        return res;
    }
};