From 2a095ae48f390fddad2506545c5b2893114f35c1 Mon Sep 17 00:00:00 2001
From: Wei Yang <richard.weiyang@gmail.com>
Date: Sun, 2 Dec 2018 09:56:35 +0800
Subject: [PATCH] implement heap in c

---
 c-cpp/28_heap/heap.c | 160 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 160 insertions(+)
 create mode 100644 c-cpp/28_heap/heap.c

diff --git a/c-cpp/28_heap/heap.c b/c-cpp/28_heap/heap.c
new file mode 100644
index 00000000..6bd872df
--- /dev/null
+++ b/c-cpp/28_heap/heap.c
@@ -0,0 +1,160 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <time.h>
+
+/* Implement heap */
+
+#define MAX_HEAP_SIZE (1 << 8)
+
+struct element {
+	int data;
+};
+
+struct heap {
+	union {
+		unsigned long elements;
+		struct element *elem[MAX_HEAP_SIZE];
+	};
+};
+
+void init_heap(struct heap *heap)
+{
+	int i;
+
+	for(i = 0; i < MAX_HEAP_SIZE; i++) {
+		heap->elem[i] = NULL;
+	}
+}
+
+void dump_heap(struct heap *heap, int index)
+{
+	struct element *elem;
+	int level;
+
+	if (index > heap->elements)
+		return;
+
+	elem = heap->elem[index];
+	level = fls(index);
+
+	dump_heap(heap, index * 2 + 1);
+
+	if (!(index % 2) && index != 1)
+		printf("%*s\n", level*3, "|");
+
+	printf("%*s - %05d\n", level*3, " ", elem->data);
+
+	if (index % 2 && index != 1)
+		printf("%*s\n", level*3, "|");
+
+	dump_heap(heap, index * 2);
+}
+
+void dump(struct heap *heap, int elements)
+{
+	int i;
+
+	for (i = 1; i <= elements; i++)
+		printf("[%02d]: %4d\n", i, heap->elem[i]->data);
+
+}
+
+struct element* create_element(int data)
+{
+	struct element *elem;
+
+	elem = malloc(sizeof(struct element));
+
+	if (elem)
+		elem->data = data;
+
+	return elem;
+}
+
+void fake_a_heap(struct heap *heap)
+{
+	/* data is in ordered */
+	int i, data[10] = {7, 4, 9, 2, 6, 8, 10, 1, 3, 5};
+
+	init_heap(heap);
+
+	/* root start at 1 */
+	for (i = 0; i < 10; i++)
+		heap->elem[i+1] = create_element(data[i]);
+
+	heap->elements = 10;
+}
+
+void swap(struct heap *heap, int i, int j)
+{
+	struct element *tmp;
+
+	tmp = heap->elem[j];
+	heap->elem[j] = heap->elem[i];
+	heap->elem[i] = tmp;
+}
+
+void heapify(struct heap *heap, int parent)
+{
+	struct element **elem = heap->elem;
+	int elements = heap->elements;
+	int left, right, max;
+
+	while (true) {
+		left = parent * 2;
+		right = left + 1;
+		
+		max = parent;
+		if (left <= elements && elem[max]->data < elem[left]->data)
+			max = left;
+		if (right <= elements && elem[max]->data < elem[right]->data)
+			max = right;
+
+		if (max == parent)
+			break;
+
+		swap(heap, max, parent);
+		parent = max;
+	}
+}
+
+void build_heap(struct heap *heap)
+{
+	int i;
+
+	for (i = heap->elements / 2; i >= 1; i--)
+		heapify(heap, i);
+}
+
+int heap_sort(struct heap *heap)
+{
+	int elements = heap->elements;
+
+	while (heap->elements) {
+		swap(heap, 1, heap->elements);
+		heap->elements--;
+		heapify(heap, 1);
+	}
+	
+	return elements;
+}
+
+int main()
+{
+	struct heap heap;
+	int elements;
+
+	fake_a_heap(&heap);
+	dump_heap(&heap, 1);
+
+	printf("After Heapify:\n");
+	build_heap(&heap);
+	dump_heap(&heap, 1);
+
+	printf("After Heap sort:\n");
+	elements = heap_sort(&heap);
+	dump(&heap, elements);
+	return 0;
+}