226 - Invert Binary Tree

#easy

Given the root of a binary tree, invert the tree, and return its root.

Example 1:

Input: root = [4,2,7,1,3,6,9]
Output: [4,7,2,9,6,3,1]

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        queue<TreeNode*> que;
        if ( root == NULL ) return NULL;
        else que.push(root);
        while ( !que.empty() ) {
            TreeNode * cur = que.front();
            que.pop();
            swap( cur -> left, cur -> right );
            if ( cur -> left != NULL ) que.push( cur -> left );
            if ( cur -> right != NULL ) que.push( cur -> right );
        }

        return root;
    }
};