 # Longest Common Subsequence

Given two strings word1 and word2, return the length of their longest common subsequence. This is often called Two Sequence Alignment Problem.

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:
``````1word1 = "abcde"
2word2 = "ace"``````
##### Explanation:

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

#### Example 2:

##### Input:
``````1word1 = "almost"
2word2 = "algomonster"``````
##### Explanation:

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

#### Example 3:

##### Input:
``````1word1 = "abc"
2word2 = "def"``````
##### Explanation:

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