101. Symmetric Tree(深搜、遞歸)

package Recursion;

public class IsSymmetric_101 {
	public class TreeNode {
		int val;
		TreeNode left;
		TreeNode right;

		TreeNode(int x) {
			val = x;
		}
	}

	public boolean isSymmetric(TreeNode root) {
		if(root==null) {
			return true;
		}
		return recur(root.left,root.right);
	}

	private boolean recur(TreeNode left, TreeNode right) {
		if(left==null&&right==null) {
			return true;
		}
		if(left==null||right==null) {
			return false;
		}
		if(left.val!=right.val) {
			return false;
		}
		
		return recur(left.left,right.right)&&recur(left.right,right.left);
	}

}