Heapsort (heapsort)

Heapsort (heapsort)

Heap Sort

1. Complete Binary Tree
2. parent > children

heapify

n = i ---> parent = (i - 1) / 2

​ ----> c1 = 2i + 1

​ ----> c2 = 2i + 2

#include <stdio.h>

void swap(int arr[], int i, int j) {
    int tmp = arr[i];
    arr[i] = arr[j];
    arr[j] = tmp;
}

void heapify(int tree[], int n, int i) {
    if (i >= n) {
        return ;
    }
    int c1 = 2 * i + 1;
    int c2 = 2 * i + 2;
    int max = i;
    if (c1 < n && tree[c1] > tree[max]) {
        max = c1;
    }
    if (c2 < n && tree[c2] > tree[max]) {
        max = c2;
    }
    if (max != i) {
        swap(tree, max, i);
        heapify(tree, n, max);
    }
}

void build_heap(int tree[], int n) {
    int last_node = n - 1;
    int parent = (last_node - 1) / 2;
    int i;
    for (i = parent; i >= 0; i--) {
        heapify(tree, n, i);
    }
}

void heap_sort(int tree[], int n) {
    build_heap(tree, n);
    int i;
    for (i = n - 1; i >= 0; i--) {
        swap(tree, i, 0);
        heapify(tree, i, 0);
    }
}

int main()
{
    int tree[] = {2, 5, 3, 1, 10, 4};
    int n = 6;
    heap_sort(tree, n);
    int i;
    for (i = 0; i < n; i++) {
        printf("%d\n",tree[i]);
    }
    return 0;
}

/* !< output */
1
2
3
4
5
10