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			30 lines
		
	
	
		
			1.2 KiB
		
	
	
	
		
			HTML
		
	
	
	
	
	
			
		
		
	
	
			30 lines
		
	
	
		
			1.2 KiB
		
	
	
	
		
			HTML
		
	
	
	
	
	
<p>Given an <code>m x n</code> integer matrix <code>heightMap</code> representing the height of each unit cell in a 2D elevation map, return <em>the volume of water it can trap after raining</em>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/04/08/trap1-3d.jpg" style="width: 361px; height: 321px;" />
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<pre>
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<strong>Input:</strong> heightMap = [[1,4,3,1,3,2],[3,2,1,3,2,4],[2,3,3,2,3,1]]
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<strong>Output:</strong> 4
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<strong>Explanation:</strong> After the rain, water is trapped between the blocks.
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We have two small ponds 1 and 3 units trapped.
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The total volume of water trapped is 4.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/04/08/trap2-3d.jpg" style="width: 401px; height: 321px;" />
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<pre>
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<strong>Input:</strong> heightMap = [[3,3,3,3,3],[3,2,2,2,3],[3,2,1,2,3],[3,2,2,2,3],[3,3,3,3,3]]
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<strong>Output:</strong> 10
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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	<li><code>m == heightMap.length</code></li>
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	<li><code>n == heightMap[i].length</code></li>
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	<li><code>1 <= m, n <= 200</code></li>
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	<li><code>0 <= heightMap[i][j] <= 2 * 10<sup>4</sup></code></li>
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</ul>
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