Symmetric Tree

1. Problem Description

Given a binary tree, check whether it is mirror-symmetric.

2. Approach

1. Approach 1
   • Preorder traversal
   • Determine whether the root’s left and right subtrees mirror each other

3. Implementation

3.1. Preorder Traversal

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isSymmetric(root *TreeNode) bool {
    if root == nil {
        return true
    }

    return isSymmetricDFS(root.Left, root.Right)
}

func isSymmetricDFS(left *TreeNode, right *TreeNode) bool {
    if left == nil && right == nil {
        return true
    }
    if left == nil || right == nil {
        return false
    }


    return left.Val == right.Val && isSymmetricDFS(left.Left, right.Right) && isSymmetricDFS(left.Right, right.Left)
}

4. References

• 101. Symmetric Tree - LeetCode