題目
給定一個(gè)二叉樹办陷，檢查它是否是鏡像對稱的私蕾。
例如猎提，二叉樹 [1,2,2,3,4,4,3] 是對稱的。
1
/ \
2 2
/ \ / \
3 4 4 3
但是下面這個(gè) [1,2,2,null,3,null,3] 則不是鏡像對稱的:
1
/ \
2 2
\ \
3 3
說明:
如果你可以運(yùn)用遞歸和迭代兩種方法解決這個(gè)問題寸五，會(huì)很加分梳凛。
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
//遞歸
public boolean isSymmetric(TreeNode root) {
return root==null || isSymmetricHelp(root.left, root.right);
}
private boolean isSymmetricHelp(TreeNode left, TreeNode right){
if(left==null || right==null)
return left==right;
if(left.val!=right.val)
return false;
return isSymmetricHelp(left.left, right.right)
&& isSymmetricHelp(left.right,right.left);
}
//非遞歸
public boolean isSymmetric1(TreeNode root) {
Queue<TreeNode> q = new LinkedList<>();
q.add(root);
q.add(root);
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.add(t1.left);
q.add(t2.right);
q.add(t1.right);
q.add(t2.left);
}
return true;
}
}
