101.go

package easy_collection

/**
 * 101. Symmetric Tree
 * <p>
 * Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
 * <p>
 * For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
 * <p>
 * 1
 * / \
 * 2   2
 * / \ / \
 * 3  4 4  3
 * <p>
 * But the following [1,2,2,null,3,null,3] is not:
 * <p>
 * 1
 * / \
 * 2   2
 * \   \
 * 3    3
 * <p>
 * Note:
 * <p>
 * Bonus points if you could solve it both recursively and iteratively.
 */

// TreeNode Definition for a binary tree node.
type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func isSymmetric(root *TreeNode) bool {
	return root == nil || helper101(root.Left, root.Right)
}

func helper101(left, right *TreeNode) bool {
	if left == nil || right == nil {
		return left == right
	}
	if left.Val != right.Val {
		return false
	}
	return helper101(left.Left, right.Right) && helper101(left.Right, right.Left)
}