Fruit Into Baskets
<p>You are visiting a farm that has a single row of fruit trees arranged from left to right. The trees are represented by an integer array <code>fruits</code> where <code>fruits[i]</code> is the <strong>type</strong> of fruit the <code>i<sup>th</sup></code> tree produces.</p>

<p>You want to collect as much fruit as possible. However, the owner has some strict rules that you must follow:</p>

<ul>
	<li>You only have <strong>two</strong> baskets, and each basket can only hold a <strong>single type</strong> of fruit. There is no limit on the amount of fruit each basket can hold.</li>
	<li>Starting from any tree of your choice, you must pick <strong>exactly one fruit</strong> from <strong>every</strong> tree (including the start tree) while moving to the right. The picked fruits must fit in one of your baskets.</li>
	<li>Once you reach a tree with fruit that cannot fit in your baskets, you must stop.</li>
</ul>

<p>Given the integer array <code>fruits</code>, return <em>the <strong>maximum</strong> number of fruits you can pick</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> fruits = [<u>1,2,1</u>]
<strong>Output:</strong> 3
<strong>Explanation:</strong> We can pick from all 3 trees.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> fruits = [0,<u>1,2,2</u>]
<strong>Output:</strong> 3
<strong>Explanation:</strong> We can pick from trees [1,2,2].
If we had started at the first tree, we would only pick from trees [0,1].
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> fruits = [1,<u>2,3,2,2</u>]
<strong>Output:</strong> 4
<strong>Explanation:</strong> We can pick from trees [2,3,2,2].
If we had started at the first tree, we would only pick from trees [1,2].
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= fruits.length &lt;= 10<sup>5</sup></code></li>
	<li><code>0 &lt;= fruits[i] &lt; fruits.length</code></li>
</ul>
Array; Hash Table; Sliding Window
use std::collections::HashMap;

impl Solution {
    pub fn total_fruit(fruits: Vec<i32>) -> i32 {
        let mut cnt = HashMap::new();
        let mut ans = 0;
        let mut j = 0;

        for (i, &x) in fruits.iter().enumerate() {
            *cnt.entry(x).or_insert(0) += 1;

            while cnt.len() > 2 {
                let y = fruits[j];
                j += 1;
                *cnt.get_mut(&y).unwrap() -= 1;
                if cnt[&y] == 0 {
                    cnt.remove(&y);
                }
            }

            ans = ans.max(i - j + 1);
        }

        ans as i32
    }
}
