The correct, optimal and working solution for programming question validate-binary-search-tree on leetcode

/* * 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 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; }