DATA STRUCTURES PROGRAM • HEAPS, HASHING & DISJOINT SETS

Build a Max-Heap from an Array

Learn how to build a max-heap from an array using a clear C program.

IntermediateMax-heapBottom-up heapifyComplete tree

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

10 5 3 4 1

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

void heapify(int values[], int size, int root)
{
    while (1) {
        int largest = root, left = 2 * root + 1, right = left + 1;
        if (left < size && values[left] > values[largest]) largest = left;
        if (right < size && values[right] > values[largest]) largest = right;
        if (largest == root) return;
        int temporary = values[root]; values[root] = values[largest]; values[largest] = temporary;
        root = largest;
    }
}

int main(void)
{
    int values[] = {4, 10, 3, 5, 1};
    int size = 5;
    for (int index = size / 2 - 1; index >= 0; index--) heapify(values, size, index);
    for (int index = 0; index < size; index++) printf("%d ", values[index]);
    putchar('\n');
    return 0;
}

CURRENT STEP

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EXPECTED OUTPUT FOR THE SAMPLE

10 5 3 4 1

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Heapify every internal node from the bottom level toward the root.
Display the computed result.

Heapify every internal node from the bottom level toward the root.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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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.