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.

• 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.

解題

func longestCommonSubsequence(text1 string, text2 string) int {
    dp := make([][]int, len(text1) + 1)
    for i := range dp {
        dp[i] = make([]int, len(text2) + 1)
    }

    for i := 1; i <= len(text1); i++ {
        for j := 1; j <= len(text2); j++ {
            // dp[i][j] = text1 前 i 個字母和 text2 前 j 個字母 最長子序列長
            if text1[i - 1] == text2[j - 1] {
                dp[i][j] = dp[i - 1][j - 1] + 1 
            } else {
                dp[i][j] = max(dp[i - 1][j], dp[i][j - 1])
            }
        }
    }

    return dp[len(text1)][len(text2)]
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}