问题描述
java实现
//way1 递归
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isSymmetric(TreeNode root) {
return isMirror(root,root);
}
private boolean isMirror(TreeNode t1, TreeNode t2){
if(t1==null && t2==null)
return true;//都为空,符合镜像
if(t1==null || t2==null)
return false;//其中都一个为空,不符合镜像
return (t1.val==t2.val) && isMirror(t1.left,t2.right) && isMirror(t1.right,t2.left);
}
}
way2:BFS
class Solution {
public boolean isSymmetric(TreeNode root) {
if (root == null)
return true;
Queue<TreeNode> q = new LinkedList<>();
q.offer(root.left);
q.offer(root.right);
while (!q.isEmpty()) {
TreeNode t1 = q.poll();
TreeNode t2 = q.poll();
if (t1 == null && t2 == null) continue;
if (t1 == null || t2 == null) return false;
if (t1.val != t2.val) return false;
q.offer(t1.left);
q.offer(t2.right);
q.offer(t1.right);
q.offer(t2.left);
}
return true;
}
}