Question

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

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

We are given the root of a binary tree with unique values, and the values x and y of two different nodes in the tree.

Return true if and only if the nodes corresponding to the values x and y are cousins.

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

Note:

1. The number of nodes in the tree will be between 2 and 100.
2. Each node has a unique integer value from 1 to 100.

Difficulty:Easy

Category:

Analyze

Solution

class Solution {
 public:
  bool isCousins(TreeNode* root, int x, int y) {
    if ((level(root, x, 1) == level(root, y, 1)) && !(isSibling(root, x, y))) return true;
    return false;
  }

 private:
  bool isSibling(TreeNode* root, int a, int b) {
    if (!root) return false;
    if (root->left && root->right) {
      if ((root->left->val == a && root->right->val == b) || (root->right->val == a && root->left->val == b)) {
        return true;
      }
    }
    return isSibling(root->left, a, b) || isSibling(root->right, a, b);
  }

  int level(TreeNode* root, int target, int lev) {
    if (!root) return 0;
    if (root->val == target) return lev;

    int l = level(root->left, target, lev + 1);
    if (l != 0) return l;
    return level(root->right, target, lev + 1);
  }
};