# VALIDATE-BINARY-SEARCH-TREE 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 i = 0;
char ch;
while((ch = getchar()) != '\n') {
str[i++] = ch;
}
str[i] = '\0';
return i;
}

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

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

int _is_valid_bst(struct node * root, long long int * m) {
if(root == NULL) {
return 1;
}

int l = _is_valid_bst(root->left, m);

if(root->val <= *m) {
return 0;
}
else {
*m = root->val;
}

int r = _is_valid_bst(root->right, m);

return l && r;
}

int is_valid_bst(struct node * root) {
long long int m = (long long int) INT_MIN - 1;
return _is_valid_bst(root, &m);
}

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

root = new_node(1);
root->left = new_node(1);
// root->right = new_node(15);
// root->right->left = new_node(6);
// root->right->right = new_node(20);

printf("%d\n", is_valid_bst(root));

return 0;
}
``````