# FLATTEN-BINARY-TREE-TO-LINKED-LIST leetcode Solution - Correct, Optimal and Working

``````/*
*  Author: Arpit Bhayani
*  https://arpitbhayani.me
*/
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <climits>
#include <deque>
#include <iostream>
#include <list>
#include <limits>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>

#define ll long long

#define MIN(a, b) a < b ? a : b
#define MAX(a, b) a > b ? a : b

using namespace std;

int readline(char *str) {
int i = 0;
char ch;
while((ch = getchar()) != '\n') {
str[i++] = ch;
}
str[i] = '\0';
return i;
}

struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
};

void flatten(struct TreeNode* root) {
struct TreeNode *node = root;
while(node) {
if(node->left) {
struct TreeNode *temp = node->left;
while(temp->right) {
temp = temp->right;
}
// temp is the rightmost in the left subtree
temp->right = node->right;
node->right = node->left;
node->left = NULL;
}
node = node->right;
}
}

struct TreeNode * new_node(int val) {
struct TreeNode *t = (struct TreeNode *) malloc(sizeof(struct TreeNode));
t->val = val;
t->left = t->right = NULL;
return t;
}

int main(int argc, char *argv[]) {
struct TreeNode * root = NULL;

root = new_node(1);
root->left = new_node(2);
root->right = new_node(5);
root->left->left = new_node(3);
root->left->right = new_node(4);
root->right->right = new_node(6);

flatten(root);

struct TreeNode * temp = root;
while(temp) {
printf("%d\n", temp->val);
temp = temp->right;
}

return 0;
}
``````