# 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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