72_binarySearchTree.c

#include<stdio.h>
#include<stdlib.h>

struct Node {
    int data;
    struct Node *left;
    struct Node *right;
};

struct Node * createNode(int data){
    struct Node *n = (struct Node *)malloc (sizeof(struct Node));
    n -> data = data;
    n -> left = NULL;
    n -> right = NULL;
    return n;
}

void inOrder(struct Node *root){
    if (root != NULL){
        inOrder(root -> left);
        printf("%d ",root -> data);
        inOrder(root -> right);
    }
}

int isBST(struct Node *root){
    static struct Node* prev = NULL;
    if(root != NULL){
        if(!isBST(root -> left)){
            return 0;
        }
        if(prev != NULL && (root -> data <= prev -> data)){
            return 0;
        }
        prev = root;
        return (isBST(root -> right));
    } else {
        return 1;
    }
}

int main(){
    struct Node* p = createNode(5);
    struct Node* p1 = createNode(3);
    struct Node* p2 = createNode(6);
    struct Node* p3 = createNode(1);
    struct Node* p4 = createNode(4);

    p -> left = p1;
    p -> right = p2;
    p1 -> left = p3;
    p1 -> right = p4;

    inOrder(p);
    printf("\n");
    printf("%d",isBST(p));
}