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C program to search an item in the binary tree using recursion

Here, we are going to learn how to search an item in the binary tree using recursion in C language?
Submitted by Nidhi, on August 24, 2021

Problem Solution:

Create a binary tree, and search an item in the binary tree using recursive function.

Program:

The source code to search an item in the binary tree using recursion is given below. The given program is compiled and executed using GCC compile on UBUNTU 18.04 OS successfully.

// C program to search an item in binary tree
// using recursion

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

typedef struct node {
    int item;
    struct node* left;
    struct node* right;

} Node;

void AddNode(Node** root, int item)
{
    Node* temp = *root;
    Node* prev = *root;

    if (*root == NULL) {
        *root = (Node*)malloc(sizeof(Node));

        (*root)->item = item;
        (*root)->left = (*root)->right = NULL;
    }
    else {
        while (temp != NULL) {
            if (item > temp->item) {
                prev = temp;
                temp = temp->right;
            }
            else {
                prev = temp;
                temp = temp->left;
            }
        }
        temp = (Node*)malloc(sizeof(Node));
        temp->item = item;

        if (item >= prev->item)
            prev->right = temp;
        else
            prev->left = temp;
    }
}

void DFS(Node* root)
{
    if (root) {
        if (root->left)
            DFS(root->left);

        if (root->right)
            DFS(root->right);

        printf("%d  ", root->item);
    }
}

int search(Node* head, int key)
{
    while (head != NULL) {
        if (key > head->item)
            return search(head->right, key);
        else if (key < head->item)
            return search(head->left, key);
        else
            return 1;
    }
    return 0;
}

int main()
{
    struct node* head = NULL;

    AddNode(&head, 10);
    AddNode(&head, 20);
    AddNode(&head, 40);
    AddNode(&head, 30);
    AddNode(&head, 60);

    printf("Tree Items:\n");
    DFS(head);
    printf("\n");

    if (search(head, 70))
        printf("%d item found in tree.\n", 70);
    else
        printf("%d item not found in tree.\n", 70);

    if (search(head, 40))
        printf("%d item found in tree.\n", 40);
    else
        printf("%d item not found in tree.\n", 40);

    return 0;
}

Output:

Tree Items:
30  60  40  20  10  
70 item not found in tree.
40 item found in tree.

Explanation:

Here, we created a self-referential structure to implement a Binary Tree, a function to add a node into the binary tree, and a recursive function search() to search a given item in the tree.

In the main() function, we created a binary search tree and called the function search() to search the given item.