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38 lines
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38 lines
1.8 KiB
HTML
<p>We run a preorder depth-first search (DFS) on the <code>root</code> of a binary tree.</p>
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<p>At each node in this traversal, we output <code>D</code> dashes (where <code>D</code> is the depth of this node), then we output the value of this node. If the depth of a node is <code>D</code>, the depth of its immediate child is <code>D + 1</code>. The depth of the <code>root</code> node is <code>0</code>.</p>
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<p>If a node has only one child, that child is guaranteed to be <strong>the left child</strong>.</p>
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<p>Given the output <code>traversal</code> of this traversal, recover the tree and return <em>its</em> <code>root</code>.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2019/04/08/recover-a-tree-from-preorder-traversal.png" style="width: 320px; height: 200px;" />
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<pre>
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<strong>Input:</strong> traversal = "1-2--3--4-5--6--7"
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<strong>Output:</strong> [1,2,5,3,4,6,7]
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</pre>
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<p><strong>Example 2:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2019/04/11/screen-shot-2019-04-10-at-114101-pm.png" style="width: 256px; height: 250px;" />
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<pre>
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<strong>Input:</strong> traversal = "1-2--3---4-5--6---7"
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<strong>Output:</strong> [1,2,5,3,null,6,null,4,null,7]
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</pre>
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<p><strong>Example 3:</strong></p>
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<img alt="" src="https://assets.leetcode.com/uploads/2019/04/11/screen-shot-2019-04-10-at-114955-pm.png" style="width: 276px; height: 250px;" />
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<pre>
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<strong>Input:</strong> traversal = "1-401--349---90--88"
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<strong>Output:</strong> [1,401,null,349,88,90]
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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 original tree is in the range <code>[1, 1000]</code>.</li>
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<li><code>1 <= Node.val <= 10<sup>9</sup></code></li>
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</ul>
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