119 lines
2.6 KiB
C
119 lines
2.6 KiB
C
/*
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Max-Heap is a binary tree structure such that every node in the tree will be
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lesser or equal to the parent node. It is used when you need quick access to
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the largest number in the array.
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Time complexity to build the heap: O(n)
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Time complexity to remove max: O(log(n))
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Time complexity to remove all elements: O(n*log(n))
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*/
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#include <stdio.h>
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#include <stdlib.h>
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struct HEAP {
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int * items, size, capacity;
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}* heap;
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void swap(int * a, int * b) {
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int temp = * b;
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* b = * a;
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* a = temp;
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}
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void init(struct HEAP ** heap) {
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* heap = (struct HEAP * ) malloc(sizeof(struct HEAP));
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( * heap) -> capacity = 2;
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( * heap) -> size = 0;
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( * heap) -> items = (int * ) malloc(sizeof(int) * ( * heap) -> capacity + 1);
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}
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void allocate(struct HEAP ** heap) {
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( * heap) -> capacity *= 2;
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( * heap) -> items = (int * ) realloc(( * heap) -> items, sizeof(int) * ( * heap) -> capacity + 1);
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}
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void heapify_up(struct HEAP ** heap, int size) {
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if (size > 1) {
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if (( * heap) -> items[size / 2] < ( * heap) -> items[size]) {
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swap( & ( * heap) -> items[size / 2], & ( * heap) -> items[size]);
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heapify_up(heap, size / 2);
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}
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}
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}
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void insert(struct HEAP ** heap, int val) {
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if (( * heap) -> size == ( * heap) -> capacity) {
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allocate(heap);
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}
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( * heap) -> items[++( * heap) -> size] = val;
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heapify_up(heap, ( * heap) -> size);
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}
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int child(struct HEAP * heap, int index) {
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int left = index * 2;
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int right = index * 2 + 1;
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if (right > heap -> size) {
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return left;
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} else if (heap -> items[left] >= heap -> items[right]) {
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return left;
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}
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return right;
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}
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void heapify_down(struct HEAP ** heap, int index) {
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int childindex = child( * heap, index);
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if (index * 2 <= ( * heap) -> size) {
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if (( * heap) -> items[index] < ( * heap) -> items[childindex]) {
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swap( & ( * heap) -> items[index], & ( * heap) -> items[childindex]);
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heapify_down(heap, childindex);
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}
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}
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}
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void removemax(struct HEAP ** heap) {
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swap( & ( * heap) -> items[1], & ( * heap) -> items[( * heap) -> size--]);
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heapify_down(heap, 1);
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}
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void print(struct HEAP * heap) {
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for (int i = 1; i <= heap -> size; i++) {
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printf("%i ", heap -> items[i]);
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}
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printf("\n");
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}
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void deallocate(struct HEAP ** heap) {
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free(( * heap) -> items);
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free( * heap);
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}
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int main(void) {
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init( & heap);
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insert( & heap, 4);
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insert( & heap, 10);
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insert( & heap, 2);
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insert( & heap, 22);
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insert( & heap, 45);
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insert( & heap, 18);
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// Before removemax
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print(heap);
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removemax( & heap);
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// After removemax
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print(heap);
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/*
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(before removemax)Output: 45 22 18 4 10 2
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(after removemax)Output: 22 10 18 4 2
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*/
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deallocate( & heap);
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return 0;
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}
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