# 84. Largest Rectangle in Histogram

## Hard

***

Given an array of integers `heights` representing the histogram's bar height where the width of each bar is `1`, return _the area of the largest rectangle in the histogram_.

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**Example 1:**

![](https://assets.leetcode.com/uploads/2021/01/04/histogram.jpg)

<pre><code>Input: heights = [2,1,5,6,2,3]
<strong>Output:
</strong> 10
<strong>Explanation:
</strong> The above is a histogram where width of each bar is 1.
The largest rectangle is shown in the red area, which has an area = 10 units.
</code></pre>

**Example 2:**

![](https://assets.leetcode.com/uploads/2021/01/04/histogram-1.jpg)

<pre><code>Input: heights = [2,4]
<strong>Output:
</strong> 4
</code></pre>

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**Constraints:**

* `1 <= heights.length <= 105`
* `0 <= heights[i] <= 104`
