LeetCode-1143. Longest Common Subsequence

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问题描述

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.

解答

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/*
 * @Description: 1143. Longest Common Subsequence
 * @Author: libk
 * @Github: https://github.com/libk
 */
/**
 * @param {string} text1
 * @param {string} text2
 * @return {number}
 */
const longestCommonSubsequence = function (text1, text2) {
  const len1 = text1.length
  const len2 = text2.length
  // 需要从空字符串的时候开始考虑，所以dp要比待处理的字符串多一位
  const dp = new Array(len1 + 1).fill(0).map(() => new Array(len2 + 1).fill(0))

  for (let i = 1; i <= len1; i++) {
    for (let j = 1; j <= len2; j++) {
      // i和j表示的是第i和第j个字符，所以在字符串中对应的下标应该是i-1和j-1
      if (text1[i - 1] === text2[j - 1]) {
        dp[i][j] = dp[i - 1][j - 1] + 1
      } else {
        dp[i][j] = Math.max(dp[i][j - 1], dp[i - 1][j])
      }
    }
  }
  return dp[len1][len2]
}