1 files changed, 152 insertions, 0 deletions

diff --git a/heap.c b/heap.c
new file mode 100644
index 0000000..365d925
--- /dev/null
+++ b/heap.c
@@ -0,0 +1,152 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include "util.h"
+
+typedef int T;
+
+// https://stackoverflow.com/a/22900767
+
+#define LEFT(idx)       (idx*2+1)
+#define RIGHT(idx)      (idx*2+2)
+#define PARENT(idx)     ((idx-1)/2)
+
+static void
+swap(T heap[], int i, int j)
+{
+        T temp  = heap[i];
+        heap[i] = heap[j];
+        heap[j] = temp;
+}
+
+static void
+fixup(T heap[], int i)
+{
+        int p = PARENT(i);
+
+        while ( i > 0 && heap[p] < heap[i] ) {
+                swap(heap, i, p);
+
+                i = p;
+                p = PARENT(i);
+        }
+}
+
+static void
+fixdown(T heap[], int i, int n)
+{
+        for ( ;; ) {
+                const int l = LEFT(i);
+                const int r = RIGHT(i);
+                int m = i;
+
+                if ( l < n && heap[m] < heap[l] )
+                        m = l;
+
+                if ( r < n && heap[m] < heap[r] )
+                        m = r;
+
+                if ( m == i )
+                        break;
+
+                swap(heap, m, i);
+
+                i = m;
+        }
+}
+
+static void
+heapify(T heap[], int n)
+{
+        for ( int i = n / 2 - 1; i >= 0; --i )
+                fixdown(heap, i, n);
+}
+
+static void
+my_heapsort(T a[], int n)
+{
+        heapify(a, n);
+
+        for ( int i = n - 1; i >= 0; --i ) {
+                swap(a, 0, i);
+                fixdown(a, 0, i);
+        }
+}
+
+// -------------------------------------------
+
+struct pq {                             // Priority Queue
+        T heap[251];
+        int sz;
+};
+
+void
+pq_init(struct pq *pq)
+{
+        pq->sz = 0;
+}
+
+bool
+pq_push(struct pq *pq, T data)
+{
+        if ( pq->sz == NELEM(pq->heap) )
+                return false;
+
+        pq->heap[pq->sz] = data;
+        fixup(pq->heap, pq->sz);
+        ++pq->sz;
+        return true;
+}
+
+bool
+pq_pop(struct pq *pq, T* data)
+{
+        if ( pq->sz == 0 )
+                return false;
+
+        *data = pq->heap[0];
+        --pq->sz;
+        pq->heap[0] = pq->heap[pq->sz];
+        fixdown(pq->heap, 0, pq->sz);
+        return true;
+}
+
+// -------------------------------------------
+
+
+void print_heap(T heap[], int n)
+{
+        if ( n ) {
+                printf("%d", heap[0]);
+                for ( int i = 1; i != n; ++i )
+                        printf(", %d", heap[i]);
+                putchar('\n');
+        }
+}
+
+int main(void)
+{
+#if 0   // Heap-Testprogramm
+        T heap[20] = { 18, 18, 16, 9, 7, 1, 9, 3, 7, 5 };
+
+        print_heap(heap, 10);
+
+        //heap[10] = 13; fixup(heap, 10);
+        swap(heap, 0, 9); fixdown(heap, 0, 9);
+
+        print_heap(heap, 9);
+#endif
+
+        struct pq pq[1];
+
+        pq_init(pq);
+
+        for ( int i = 0; i != 10; ++i )
+                pq_push(pq, rand());
+
+        T data;
+        while ( pq_pop(pq, &data) )
+                printf("%d\n", data);
+}
+
+