/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(root ==nullptr ) return root;
        queue<TreeNode*>qu; //这里是用到了层序遍历 所以需要一个队列
        qu.push(root);
        while(!qu.empty())
        {
            TreeNode * node = qu.front();
            qu.pop();
            if(node->left!=nullptr) qu.push(node->left);//把左子节点放入队列 
            if(node->right!=nullptr) qu.push(node->right);//把右子节点放入队列
            
            //交换已经不再队列的node的左右指针
            TreeNode* temp = node->left;
            node->left = node -> right;
            node -> right = temp;
            
        }
        return root;
    }
};