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
/**
* 递归
* 时间复杂度:O(n)
* 空间复杂度:O(n)
*/
var isSymmetric = function (root) {
if (!root === null) return true
return compare(root.left, root.right)
}
function compare(left, right) {
if (left === null && right === null) return true
if (left === null || right === null) return false
return (
left.val === right.val &&
compare(left.left, right.right) &&
compare(left.right, right.left)
)
}
/**
* 广度遍历
* 时间复杂度:O(n)
* 空间复杂度:O(n)
*/
var isSymmetric = function (root) {
const stack = [root.left, root.right]
while (stack.length) {
const right = stack.pop()
const left = stack.pop()
if (left && right) {
if (left.val !== right.val) {
return false
}
stack.push(left.left)
stack.push(right.right)
stack.push(left.right)
stack.push(right.left)
} else if (left || right) {
return false
}
}
return true
}