Initialize

heap.c

@@ -0,0 +1,112 @@
+#include "dat.h"
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+static void
+set(Heap *h, size_t k, void *x)
+{
+    h->data[k] = x;
+    h->setpos(x, k);
+}
+
+
+static void
+swap(Heap *h, size_t a, size_t b)
+{
+    void *tmp;
+
+    tmp = h->data[a];
+    set(h, a, h->data[b]);
+    set(h, b, tmp);
+}
+
+
+static int
+less(Heap *h, size_t a, size_t b)
+{
+    return h->less(h->data[a], h->data[b]);
+}
+
+
+static void
+siftdown(Heap *h, size_t k)
+{
+    for (;;) {
+        size_t p = (k-1) / 2; /* parent */
+
+        if (k == 0 || less(h, p, k)) {
+            return;
+        }
+
+        swap(h, k, p);
+        k = p;
+    }
+}
+
+
+static void
+siftup(Heap *h, size_t k)
+{
+    for (;;) {
+        size_t l = k*2 + 1; /* left child */
+        size_t r = k*2 + 2; /* right child */
+
+        /* find the smallest of the three */
+        size_t s = k;
+        if (l < h->len && less(h, l, s)) s = l;
+        if (r < h->len && less(h, r, s)) s = r;
+
+        if (s == k) {
+            return; /* satisfies the heap property */
+        }
+
+        swap(h, k, s);
+        k = s;
+    }
+}
+
+
+// Heapinsert inserts x into heap h according to h->less.
+// It returns 1 on success, otherwise 0.
+int
+heapinsert(Heap *h, void *x)
+{
+    if (h->len == h->cap) {
+        void **ndata;
+        size_t ncap = (h->len+1) * 2; /* allocate twice what we need */
+
+        ndata = malloc(sizeof(void*) * ncap);
+        if (!ndata) {
+            return 0;
+        }
+
+        memcpy(ndata, h->data, sizeof(void*) * h->len);
+        free(h->data);
+        h->data = ndata;
+        h->cap = ncap;
+    }
+
+    size_t k = h->len;
+    h->len++;
+    set(h, k, x);
+    siftdown(h, k);
+    return 1;
+}
+
+
+void *
+heapremove(Heap *h, size_t k)
+{
+    if (k >= h->len) {
+        return 0;
+    }
+
+    void *x = h->data[k];
+    h->len--;
+    set(h, k, h->data[h->len]);
+    siftdown(h, k);
+    siftup(h, k);
+    return x;
+}