给定一个二叉树,检查它是否是镜像对称的。
本题需要同时遍历两棵树,一棵树的顺序是左右中,另一棵是右左中
递归三部曲:
func isSame(left *TreeNode, right *TreeNode) bool
if left == nil && right != nil return false
else if left != nil && right == nil return false
else if left == nil && right == nil return true
else if left.Val != right.Val return false
也可以写成
if left == nil && right = nil return true
if root == nil || right == nil return false
if left.Val != right.Val return false
// 左子树:左右中 右子树:右左中
outside := compare(left.Left, right.Right)
inside := compare(left.Right, right.Left)
isSame := outside && inside
return isSame
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func isSymmetric(root *TreeNode) bool {
if root == nil {
return true
}
return isSameTree(root.Left,root.Right)
}
func isSameTree(p *TreeNode,q *TreeNode) bool {
if p == nil && q == nil {
return true
}
if p == nil || q == nil {
return false
}
if p.Val != q.Val {
return false
}
outSide := isSameTree(p.Left,q.Right)
inSide := isSameTree(p.Right,q.Left)
return outSide && inSide
}
本题的本质是判断两个树是否相互反转,已经不是纯粹的前中后序的关系了
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func isSymmetric(root *TreeNode) bool {
if root == nil {
return true
}
queue := []*TreeNode{}
queue = append(queue, root.Left)
queue = append(queue, root.Right)
for len(queue) > 0 {
leftNode := queue[0]
rightNode := queue[1]
queue = queue[2:]
if leftNode == nil && rightNode == nil {
continue
}
if leftNode == nil || rightNode == nil {
return false
}
if leftNode.Val != rightNode.Val {
return false
}
queue = append(queue, leftNode.Left)
queue = append(queue, rightNode.Right)
queue = append(queue,leftNode.Right)
queue = append(queue, rightNode.Left)
}
return true
}