Longest Common Subsequence

Given two strings word1 and word2, return the length of their longest common subsequence.

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. (eg, "ace" is a subsequence of "abcde" while "aec" is not). A common subsequence of two strings is a subsequence that is common to both strings.

If there is no common subsequence, return 0.

Example 1:

Input:
word1 = "abcde"
word2 = "ace"
Output: 3
Explanation:

The longest common subsequence is ace and its length is 3.

Example 2:

Input:
word1 = "almost"
word2 = "algomonster"
Output: 6
Explanation:

The longest common subsequence is almost and its length is 6.

Example 3:

Input:
word1 = "abc"
word2 = "def"
Output: 0
Explanation:

There is no such common subsequence, so the result is 0.

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