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

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

void insertIntoBSTRecursively(struct TreeNode*, int);

struct TreeNode* insertIntoBST(struct TreeNode* root, int val) {
    insertIntoBSTRecursively(root, val);
    return root;
}

void insertIntoBSTRecursively(struct TreeNode* tree, int val) {
    if (val < tree->val) {
        // Go left if possible
        // else append a new TreeNode with this value
        if (tree->left != NULL) {
            insertIntoBSTRecursively(tree->left, val);
        } else {
            struct TreeNode *t = malloc(sizeof(struct TreeNode));
            t->val = val;
            t->left = NULL;
            t->right = NULL;
            tree->left = t;
        }
    } else {
        // Go right if possible
        // else append a new TreeNode with this value
        if (tree->right != NULL) {
            insertIntoBSTRecursively(tree->right, val);
        } else {
            struct TreeNode *t = malloc(sizeof(struct TreeNode));
            t->val = val;
            t->left = NULL;
            t->right = NULL;
            tree->right = t;
        }
    }
}

int main() {
    struct TreeNode *t2 = malloc(sizeof(struct TreeNode));
    t2->val = 2;
    t2->left = NULL;
    t2->right = NULL;
    struct TreeNode *t3 = malloc(sizeof(struct TreeNode));
    t3->val = 3;
    t3->left = NULL;
    t3->right = NULL;
    struct TreeNode *t = malloc(sizeof(struct TreeNode));
    t->val = 1;
    t->left = t2;
    t->right = t3;
    printf("Expecting to add value `4` to tree...\n");
    insertIntoBST(t, 4);
    // Here check t contains 4 now.
    if (t->right->right->val == 4) {
        printf("Value `4` added to Tree!\n");
        return 0;
    }
    return -1;
}