Day73.java

class TreeNode {
    int val;
    TreeNode left, right;
    
    public TreeNode(int val) {
        this.val = val;
        this.left = this.right = null;
    }
}
public class Day73 {

    public boolean isSymmetric(TreeNode root) {
        if (root == null) return true;
        return isMirror(root.left, root.right);
    }
    private boolean isMirror(TreeNode left, TreeNode right) {
        if (left == null && right == null) return true;
        if (left == null || right == null) return false;
        return (left.val == right.val) && isMirror(left.left, right.right) && isMirror(left.right, right.left);
    }
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left = new TreeNode(2);
        root.right = new TreeNode(2);
        root.left.left = new TreeNode(3);
        root.left.right = new TreeNode(4);
        root.right.left = new TreeNode(4);
        root.right.right = new TreeNode(3);

        SymmetricTree symmetricTree = new SymmetricTree();
        boolean isSymmetric = symmetricTree.isSymmetric(root);
        System.out.println("Is the binary tree symmetric? " + isSymmetric);
    }
}