力扣226：翻转二叉树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
void swap(struct TreeNode**left,struct TreeNode**right)
{
    struct TreeNode*tmp=*left;
    *left=*right;
    *right=tmp;
}
struct TreeNode* invertTree(struct TreeNode* root) {
    if(root==NULL)
        return NULL;
    swap(&root->left,&root->right);
    invertTree(root->left);
    invertTree(root->right);
    return root;
}