951. Flip Equivalent Binary Trees

Description

For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees.

A binary tree X is flip equivalent to a binary tree Y if and only if we can make X equal to Y after some number of flip operations.

Given the roots of two binary trees root1 and root2, return true if the two trees are flip equivalent or false otherwise.

 

Example 1:

Input: root1 = [1,2,3,4,5,6,null,null,null,7,8], root2 = [1,3,2,null,6,4,5,null,null,null,null,8,7]
Output: true
Explanation: We flipped at nodes with values 1, 3, and 5.

Example 2:

Input: root1 = [], root2 = []
Output: true

Example 3:

Input: root1 = [], root2 = [1]
Output: false

 

Constraints:

• The number of nodes in each tree is in the range [0, 100].
• Each tree will have unique node values in the range [0, 99].

 

Solutions

Solution: Depth-First Search

• Time complexity: O(n)
• Space complexity: O(n)

 

JavaScript

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root1
 * @param {TreeNode} root2
 * @return {boolean}
 */
const flipEquiv = function (root1, root2) {
  const flipToEquivalentTree = (node1, node2) => {
    if (!node1 && !node2) return true;
    if (!node1 || !node2) return false;
    if (node1.val !== node2.val) return false;

    const { left, right } = node1;

    if (left?.val !== node2.left?.val) {
      node1.right = left;
      node1.left = right;
    }
    const isLeftEquivalent = flipToEquivalentTree(node1.left, node2.left);
    const isRightEquivalent = flipToEquivalentTree(node1.right, node2.right);

    return isLeftEquivalent && isRightEquivalent;
  };

  return flipToEquivalentTree(root1, root2);
};