The correct, optimal and working solution for programming question is-binary-search-tree on hackerrank

/* * 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 data; struct node * left; struct node * right; }; struct node * new_node(int v) { struct node * t = (struct node *) calloc(1, sizeof(struct node)); t->data = v; return t; } bool _check(struct node * root, int * m) { if(root == NULL) { return true; } bool l = _check(root->left, m); if(root->data <= *m) { return false; } *m = root->data; bool r = _check(root->right, m); return l && r; } bool checkBST(struct node * root) { int m = -1; return _check(root, &m); } int main(int argc, char *argv[]) { struct node * root = new_node(3); root->left = new_node(1); root->right = new_node(4); printf("%d\n", checkBST(root)); return 0; }