101. Symmetric Tree.md

Solution1

class Solution {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) {
            return true;
        }
        return isSymmetric(root.left, root.right);
    }
    private boolean isSymmetric(TreeNode t1, TreeNode t2) {
        if (t1 == null && t2 == null) {
            return true;
        }
        if (t1 == null || t2 == null) {
            return false;
        }
        if (t1.val != t2.val) {
            return false;
        }
        return isSymmetric(t1.left, t2.right) && isSymmetric(t1.right, t2.left);
    }
}

note

• Recursion, use helper function to check recursively its subtrees