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35 lines
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35 lines
1.8 KiB
HTML
<p>One way to serialize a binary tree is to use <strong>preorder traversal</strong>. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as <code>'#'</code>.</p>
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<img alt="" src="https://assets.leetcode.com/uploads/2021/03/12/pre-tree.jpg" style="width: 362px; height: 293px;" />
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<p>For example, the above binary tree can be serialized to the string <code>"9,3,4,#,#,1,#,#,2,#,6,#,#"</code>, where <code>'#'</code> represents a null node.</p>
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<p>Given a string of comma-separated values <code>preorder</code>, return <code>true</code> if it is a correct preorder traversal serialization of a binary tree.</p>
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<p>It is <strong>guaranteed</strong> that each comma-separated value in the string must be either an integer or a character <code>'#'</code> representing null pointer.</p>
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<p>You may assume that the input format is always valid.</p>
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<ul>
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<li>For example, it could never contain two consecutive commas, such as <code>"1,,3"</code>.</li>
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</ul>
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<p><strong>Note: </strong>You are not allowed to reconstruct the tree.</p>
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<p> </p>
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<p><strong>Example 1:</strong></p>
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<pre><strong>Input:</strong> preorder = "9,3,4,#,#,1,#,#,2,#,6,#,#"
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<strong>Output:</strong> true
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</pre><p><strong>Example 2:</strong></p>
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<pre><strong>Input:</strong> preorder = "1,#"
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<strong>Output:</strong> false
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</pre><p><strong>Example 3:</strong></p>
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<pre><strong>Input:</strong> preorder = "9,#,#,1"
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<strong>Output:</strong> false
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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>1 <= preorder.length <= 10<sup>4</sup></code></li>
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<li><code>preorder</code> consist of integers in the range <code>[0, 100]</code> and <code>'#'</code> separated by commas <code>','</code>.</li>
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</ul>
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