Link: https://leetcode.cn/problems/cousins-in-binary-tree/

Question

difficulty: easy
adj diff: 3

Given the root of a binary tree with unique values and the values of two different nodes of the tree x and y, return true if the nodes corresponding to the values x and y in the tree are cousins, or false otherwise.

Two nodes of a binary tree are cousins if they have the same depth with different parents.

Note that in a binary tree, the root node is at the depth 0, and children of each depth k node are at the depth k + 1.

Example 1:

Input: root = [1,2,3,4], x = 4, y = 3
Output: false

Example 2:

Input: root = [1,2,3,null,4,null,5], x = 5, y = 4
Output: true

Example 3:

Input: root = [1,2,3,null,4], x = 2, y = 3
Output: false

Constraints:

	The number of nodes in the tree is in the range [2, 100].
	1 <= Node.val <= 100
	Each node has a unique value.
	x != y
	x and y are exist in the tree.

解法非常地类似 LCA 经典解法。

Code

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public boolean isCousins(TreeNode root, int x, int y) {
    int res = depth(0, root, x, y);
    return res == Integer.MAX_VALUE;
}

private int depth(int level, TreeNode node, int x, int y) {
    if (node == null) {
        return -1;
    } else if (node.val == x || node.val == y) {
        return level;
    }

    int ll = depth(level + 1, node.left, x, y);
    int rr = depth(level + 1, node.right, x, y);
    if (ll == -1 && rr == -1) {
        return -1;
    } else if (ll == -1) {
        return rr;
    } else if (rr == -1) {
        return ll;
    } else {
        return ll == rr && ll - level > 1 ? Integer.MAX_VALUE : -1;
    }
}