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LeetCode101.java

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package problems;

import java.util.LinkedList;

/**

* DFS

*/

public class LeetCode101 {

public boolean isSymmetric(TreeNode root) {

return dfs(root.left, root.right);

}

private boolean dfs(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 dfs(left.right, right.left) && dfs(left.left, right.right);

}

}

/**

* 队列

*/

class LeetCode101_1 {

public boolean isSymmetric(TreeNode root) {

if(root==null || (root.left==null && root.right==null)) {

return true;

}

//用队列保存节点

LinkedList<TreeNode> queue = new LinkedList<TreeNode>();

//将根节点的左右孩子放到队列中

queue.add(root.left);

queue.add(root.right);

while(queue.size()>0) {

//从队列中取出两个节点，再比较这两个节点

TreeNode left = queue.removeFirst();

TreeNode right = queue.removeFirst();

//如果两个节点都为空就继续循环，两者有一个为空就返回false

if(left==null && right==null) {

continue;

}

if(left==null || right==null) {

return false;

}

if(left.val!=right.val) {

return false;

}

//将左节点的左孩子， 右节点的右孩子放入队列

queue.add(left.left);

queue.add(right.right);

//将左节点的右孩子，右节点的左孩子放入队列

queue.add(left.right);

queue.add(right.left);

}

return true;

}

}