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101. 对称二叉树.js
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101. 对称二叉树.js
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/**
101. 对称二叉树
给定一个二叉树,检查它是否是镜像对称的。
例如,二叉树 [1,2,2,3,4,4,3] 是对称的。
1
/ \
2 2
/ \ / \
3 4 4 3
但是下面这个 [1,2,2,null,3,null,3] 则不是镜像对称的:
1
/ \
2 2
\ \
3 3
进阶:
你可以运用递归和迭代两种方法解决这个问题吗?
*/
/**
* 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) {
if (!root) return true;
return dfs(root.left, root.right);
};
function dfs(left, right) {
if (!left && !right) return true;
if (!left || !right) return false;
return (
left.val === right.val &&
dfs(left.left, right.right) &&
dfs(left.right, right.left)
);
}
//广度优先遍历
var isSymmetric = function (root) {
if (!root) return true;
return bfs(root.left, root.right);
};
function bfs(left, right) {
let queue = [left, right];
while (queue.length) {
let left = queue.shift();
let right = queue.shift();
if (left && right) {
if (left.val !== right.val) return false;
queue.push(left.left, right.right);
queue.push(left.right, right.left);
} else if (left || right) {
return false;
}
}
return true;
}