DATA STRUCTURES PROGRAM • TREES & BINARY SEARCH TREES

Traverse a Binary Tree Preorder Recursively

Learn how to traverse a binary tree preorder recursively using a clear C program.

BeginnerBinary treeNodesRecursion

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

1 2 4 5 3 6 7

COMPLETE C PROGRAM

Complete C implementation

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

struct TreeNode { int data; struct TreeNode *left; struct TreeNode *right; };
struct TreeNode *new_node(int value)
{
    struct TreeNode *node = malloc(sizeof *node);
    if (node == NULL) exit(EXIT_FAILURE);
    node->data = value; node->left = NULL; node->right = NULL;
    return node;
}
struct TreeNode *sample_tree(void)
{
    struct TreeNode *root = new_node(1);
    root->left = new_node(2); root->right = new_node(3);
    root->left->left = new_node(4); root->left->right = new_node(5);
    root->right->left = new_node(6); root->right->right = new_node(7);
    return root;
}
void free_tree(struct TreeNode *root)
{
    if (root == NULL) return;
    free_tree(root->left); free_tree(root->right); free(root);
}
void preorder(struct TreeNode *root)
{
    if (root == NULL) return;
    printf("%d ", root->data); preorder(root->left); preorder(root->right);
}

int main(void)
{
    struct TreeNode *root = sample_tree();
    preorder(root); putchar('\n');
    free_tree(root);
    return 0;
}

CURRENT STEP

Select Start to walk through the important lines.

SELECTED LINE

No line selected

EXPECTED OUTPUT FOR THE SAMPLE

1 2 4 5 3 6 7

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Process the current node before recursively traversing its two subtrees.
Display the computed result.

Process the current node before recursively traversing its two subtrees.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(h)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.