Invert a Binary Tree

#include <bits/stdc++.h> 
/************************************************************

    Following is the TreeNode class structure

    template <typename T>
    class TreeNode {
       public:
        T data;
        TreeNode<T> *left;
        TreeNode<T> *right;

        TreeNode(T data) {
            this->data = data;
            left = NULL;
            right = NULL;
        }
    };

************************************************************/

void invert(TreeNode<int>* root, TreeNode<int>* parent, TreeNode<int>* leaf, TreeNode<int>* &ans, bool &flag)
{
    if(!root) return;

    if(root->data==leaf->data){
        root->left=parent;
        flag=true;
        ans=root;
        return;
    }

    invert(root->left,root,leaf,ans,flag);

    if(flag){
        root->left=parent;
        return;
    }

    invert(root->right,root,leaf,ans,flag);

    if(flag){
        if(root->left) root->right=root->left;
        else root->right=NULL;
        root->left=parent;
        return;
    }
}


TreeNode<int> * invertBinaryTree(TreeNode<int> *root, TreeNode<int> *leaf)
{
    bool flag=false;
	TreeNode<int>* ans=NULL;
    invert(root,NULL,leaf,ans,flag);
    return ans; 
}