Merge pull request #1243 from karthikyandrapu/max_heap

Added Max Heap

Heaps/Max Heap/Program.c

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+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct max_heap {
+    int *p;
+    int size;
+    int count;
+} Heap;
+
+Heap *create_heap(Heap *heap); // Initializes a new heap
+void down_heapify(Heap *heap, int index); // Restores max-heap property from the specified index downwards
+void up_heapify(Heap *heap, int index); // Restores max-heap property from the specified index upwards
+void push(Heap *heap, int x); // Inserts a new element into the heap
+void pop(Heap *heap); // Removes the maximum element from the heap
+int top(Heap *heap); // Retrieves the maximum element of the heap
+int empty(Heap *heap); // Checks if the heap is empty
+int size(Heap *heap); // Returns the current number of elements in the heap
+
+int main() {
+    Heap *head = create_heap(head);
+    push(head, 10);
+    printf("Pushing element : 10\n");
+    push(head, 3);
+    printf("Pushing element : 3\n");
+    push(head, 2);
+    printf("Pushing element : 2\n");
+    push(head, 8);
+    printf("Pushing element : 8\n");
+    printf("Top element = %d \n", top(head));
+    push(head, 1);
+    printf("Pushing element : 1\n");
+    push(head, 7);
+    printf("Pushing element : 7\n");
+    printf("Top element = %d \n", top(head));
+    pop(head);
+    printf("Popping an element.\n");
+    printf("Top element = %d \n", top(head));
+    pop(head);
+    printf("Popping an element.\n");
+    printf("Top element = %d \n", top(head));
+    printf("\n");
+    return 0;
+}
+
+Heap *create_heap(Heap *heap) {
+    // Allocate memory for the heap and initialize its properties
+    heap = (Heap *)malloc(sizeof(Heap));
+    heap->size = 2; // Initial capacity of the heap array
+    heap->p = (int *)malloc(heap->size * sizeof(int));
+    heap->count = 0;
+    return heap;
+}
+
+void down_heapify(Heap *heap, int index) {
+    // Reorder the heap starting from the specified index downwards
+    if (index >= heap->count) return;
+    int left = index * 2 + 1;
+    int right = index * 2 + 2;
+    int largest = index;
+
+    if (left < heap->count && heap->p[left] > heap->p[largest])
+        largest = left;
+    if (right < heap->count && heap->p[right] > heap->p[largest])
+        largest = right;
+    if (largest != index) {
+        int temp = heap->p[largest];
+        heap->p[largest] = heap->p[index];
+        heap->p[index] = temp;
+        down_heapify(heap, largest);
+    }
+}
+
+void up_heapify(Heap *heap, int index) {
+    // Move element at index up to restore heap property
+    int parent = (index - 1) / 2;
+    if (parent >= 0 && heap->p[index] > heap->p[parent]) {
+        int temp = heap->p[index];
+        heap->p[index] = heap->p[parent];
+        heap->p[parent] = temp;
+        up_heapify(heap, parent);
+    }
+}
+
+void push(Heap *heap, int x) {
+    // Insert an element into the heap, resizing if necessary
+    if (heap->count == heap->size) {
+        heap->size *= 2;
+        heap->p = (int *)realloc(heap->p, heap->size * sizeof(int));
+    }
+    heap->p[heap->count++] = x;
+    up_heapify(heap, heap->count - 1);
+}
+
+void pop(Heap *heap) {
+    // Remove the top (max) element and reorder the heap
+    if (heap->count == 0) return;
+    heap->count--;
+    heap->p[0] = heap->p[heap->count];
+    down_heapify(heap, 0);
+    // Shrink array if necessary
+    if (heap->count > 0 && heap->count <= heap->size / 4) {
+        heap->size /= 2;
+        heap->p = (int *)realloc(heap->p, heap->size * sizeof(int));
+    }
+}
+
+int top(Heap *heap) {
+    // Return max element or INT_MIN if heap is empty
+    return heap->count != 0 ? heap->p[0] : INT_MIN;
+}
+
+int empty(Heap *heap) {
+    return heap->count == 0;
+}
+
+int size(Heap *heap) {
+    return heap->count;
+}

Heaps/Max Heap/README.md

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+
+# Heap Implementation in C
+
+This document provides a detailed explanation of a max-heap data structure implemented in C. This implementation includes functions to insert, remove, and retrieve the maximum element, along with other utility functions.
+
+## Code Overview
+
+This code defines a struct `max_heap` which is used to represent a max-heap. A max-heap is a complete binary tree in which each node is greater than or equal to its child nodes. The implementation uses an array for efficient indexing.
+
+### Struct Definition
+```c
+typedef struct max_heap {
+    int *p;
+    int size;
+    int count;
+} Heap;
+```
+- `p`: Pointer to an array representing the heap.
+- `size`: Current allocated size of the array.
+- `count`: Current number of elements in the heap.
+
+### Functions
+
+#### 1. `create_heap(Heap *heap)`
+Creates a new max-heap with an initial capacity of 2. Returns a pointer to the heap structure.
+
+#### 2. `down_heapify(Heap *heap, int index)`
+Restores the max-heap property by moving the element at the given `index` downwards.
+
+#### 3. `up_heapify(Heap *heap, int index)`
+Moves the element at the given `index` upwards to maintain the max-heap property.
+
+#### 4. `push(Heap *heap, int x)`
+Inserts a new element `x` into the heap. Resizes the heap array if the current capacity is reached.
+
+#### 5. `pop(Heap *heap)`
+Removes the top (maximum) element from the heap and reorders the remaining elements.
+
+#### 6. `top(Heap *heap)`
+Returns the maximum element in the heap. Returns `INT_MIN` if the heap is empty.
+
+#### 7. `empty(Heap *heap)`
+Checks if the heap is empty.
+
+#### 8. `size(Heap *heap)`
+Returns the number of elements currently in the heap.
+
+### Example Usage
+
+```c
+Heap *head = create_heap(head);
+push(head, 10);
+push(head, 3);
+push(head, 2);
+push(head, 8);
+printf("Top element = %d 
+", top(head));
+pop(head);
+printf("After popping, Top element = %d 
+", top(head));
+```
+
+### Complexity Analysis
+
+#### Time Complexity
+
+| Operation | Time Complexity |
+|-----------|-----------------|
+| `push`    | O(log n)        |
+| `pop`     | O(log n)        |
+| `top`     | O(1)            |
+
+- `push` and `pop` involve heapification, which takes `O(log n)` time as elements are moved up or down in the heap.
+- `top` is `O(1)` because it only retrieves the maximum element.
+
+#### Space Complexity
+- The space complexity is `O(n)`, where `n` is the number of elements in the heap. Additional memory is used only if the array needs to be resized.
+
+### Notes
+- The max-heap property is maintained by comparing elements while inserting or deleting nodes.
+- Dynamic resizing allows efficient memory usage while maintaining performance.
+
+## Conclusion
+
+This implementation provides efficient methods for a max-heap in C, ideal for priority queue operations where fast access to the maximum element is required.
+