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39 lines
2.0 KiB
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<p>You are given a tree with <code>n</code> nodes numbered from <code>0</code> to <code>n - 1</code> in the form of a parent array <code>parent</code> where <code>parent[i]</code> is the parent of <code>i<sup>th</sup></code> node. The root of the tree is node <code>0</code>. Find the <code>k<sup>th</sup></code> ancestor of a given node.</p>
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<p>The <code>k<sup>th</sup></code> ancestor of a tree node is the <code>k<sup>th</sup></code> node in the path from that node to the root node.</p>
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<p>Implement the <code>TreeAncestor</code> class:</p>
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<ul>
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<li><code>TreeAncestor(int n, int[] parent)</code> Initializes the object with the number of nodes in the tree and the parent array.</li>
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<li><code>int getKthAncestor(int node, int k)</code> return the <code>k<sup>th</sup></code> ancestor of the given node <code>node</code>. If there is no such ancestor, return <code>-1</code>.</li>
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</ul>
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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/2019/08/28/1528_ex1.png" style="width: 396px; height: 262px;" />
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<pre>
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<strong>Input</strong>
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["TreeAncestor", "getKthAncestor", "getKthAncestor", "getKthAncestor"]
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[[7, [-1, 0, 0, 1, 1, 2, 2]], [3, 1], [5, 2], [6, 3]]
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<strong>Output</strong>
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[null, 1, 0, -1]
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<strong>Explanation</strong>
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TreeAncestor treeAncestor = new TreeAncestor(7, [-1, 0, 0, 1, 1, 2, 2]);
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treeAncestor.getKthAncestor(3, 1); // returns 1 which is the parent of 3
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treeAncestor.getKthAncestor(5, 2); // returns 0 which is the grandparent of 5
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treeAncestor.getKthAncestor(6, 3); // returns -1 because there is no such ancestor</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 <= k <= n <= 5 * 10<sup>4</sup></code></li>
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<li><code>parent.length == n</code></li>
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<li><code>parent[0] == -1</code></li>
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<li><code>0 <= parent[i] < n</code> for all <code>0 < i < n</code></li>
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<li><code>0 <= node < n</code></li>
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<li>There will be at most <code>5 * 10<sup>4</sup></code> queries.</li>
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</ul>
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