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Solution.java
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Solution.java
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package easy._101;
import structure.TreeNode;
import java.util.Deque;
import java.util.LinkedList;
/**
* @author zmj
* @Description 检查一颗二叉树是否对称
* @create 2018/9/27
*/
public class Solution {
/**
* 递归方法
*/
public boolean isSymmetric(TreeNode root) {
if (root == null) return true;
return checkIsSymmetric(root.left, root.right);
}
private boolean checkIsSymmetric(TreeNode left, TreeNode right) {
if (left == null && right == null) return true;
if (left == null || right == null) return false;
if (left.val != right.val) return false;
return checkIsSymmetric(left.left, right.right) && checkIsSymmetric(left.right, right.left);
}
/**
* 迭代方法
* 思路,层序遍历,双端队列
*/
public boolean isSymmetric2(TreeNode root) {
if (root == null) return true;
Deque<TreeNode> deque = new LinkedList<>();
deque.offerFirst(root.left);
deque.offerFirst(root.right);
TreeNode preNode = null;
TreeNode postNode = null;
while (!deque.isEmpty()) {
preNode = deque.pollFirst();
postNode = deque.pollLast();
}
return true;
}
}