1483. Kth Ancestor of a Tree Node ¶

Problem

You are given a tree with n nodes numbered from 0 to n - 1 in the form of a parent array parent where parent[i] is the parent of i^th node. The root of the tree is node 0. Find the k^th ancestor of a given node.

The k^th ancestor of a tree node is the k^th node in the path from that node to the root node.

Implement the TreeAncestor class:

TreeAncestor(int n, int[] parent) Initializes the object with the number of nodes in the tree and the parent array.
int getKthAncestor(int node, int k) return the k^th ancestor of the given node node. If there is no such ancestor, return -1.

Example 1:

Input
["TreeAncestor", "getKthAncestor", "getKthAncestor", "getKthAncestor"]
[[7, [-1, 0, 0, 1, 1, 2, 2]], [3, 1], [5, 2], [6, 3]]
Output
[null, 1, 0, -1]

Explanation
TreeAncestor treeAncestor = new TreeAncestor(7, [-1, 0, 0, 1, 1, 2, 2]);
treeAncestor.getKthAncestor(3, 1); // returns 1 which is the parent of 3
treeAncestor.getKthAncestor(5, 2); // returns 0 which is the grandparent of 5
treeAncestor.getKthAncestor(6, 3); // returns -1 because there is no such ancestor

Constraints:

1 <= k <= n <= 5 * 10⁴
parent.length == n
parent[0] == -1
0 <= parent[i] < n for all 0 < i < n
0 <= node < n
There will be at most 5 * 10⁴ queries.