Description:
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
1
/ \
2 2
/ \ / \
3 4 4 3
But the following [1,2,2,null,3,null,3] is not:
1
/ \
2 2
\ \
3 3
My code:
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {boolean}
*/
var isSymmetric = function(root) {
return checkEquality(root, root);
};
var checkEquality = function(left, right) {
if(left && right) { // 非叶子节点处理
if(left.val == right.val) {
return checkEquality(left.left, right.right) && checkEquality(left.right, right.left);
} else {
return false;
}
} else if(left == right) { // 判断叶子值是否相等
return true;
} else {
return false;
}
}
Note: 跟100. Same Tree 思路差不多，100是两个树对比，本题可以看作自己与自己的副本对比
