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29 lines
1.3 KiB
HTML
29 lines
1.3 KiB
HTML
<p>You are given the <code>root</code> of a binary tree. We install cameras on the tree nodes where each camera at a node can monitor its parent, itself, and its immediate children.</p>
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<p>Return <em>the minimum number of cameras needed to monitor all nodes of the tree</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/2018/12/29/bst_cameras_01.png" style="width: 138px; height: 163px;" />
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<pre>
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<strong>Input:</strong> root = [0,0,null,0,0]
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<strong>Output:</strong> 1
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<strong>Explanation:</strong> One camera is enough to monitor all nodes if placed as shown.
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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/2018/12/29/bst_cameras_02.png" style="width: 139px; height: 312px;" />
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<pre>
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<strong>Input:</strong> root = [0,0,null,0,null,0,null,null,0]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> At least two cameras are needed to monitor all nodes of the tree. The above image shows one of the valid configurations of camera placement.
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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>The number of nodes in the tree is in the range <code>[1, 1000]</code>.</li>
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<li><code>Node.val == 0</code></li>
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</ul>
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