Initial data commit

Task/Priority-queue/C/priority-queue-3.c

@@ -0,0 +1,44 @@
+#include <stdlib.h>
+#include "pairheap.h"
+
+/* ---------------------------------------------------------------------------
+ * Pairing heap implementation
+ * --------------------------------------------------------------------------- */
+
+static heap_t add_child(heap_t h, heap_t g) {
+    if (h->down != NULL)
+        g->next = h->down;
+    h->down = g;
+}
+
+heap_t heap_merge(heap_t a, heap_t b) {
+    if (a == NULL) return b;
+    if (b == NULL) return a;
+    if (a->key < b->key) {
+        add_child(a, b);
+        return a;
+    } else {
+        add_child(b, a);
+        return b;
+    }
+}
+
+/* NOTE: caller should have pointer to top of heap, since otherwise it won't
+ *       be reclaimed.  (we do not free the top.)
+ */
+heap_t two_pass_merge(heap_t h) {
+    if (h == NULL || h->next == NULL)
+        return h;
+    else {
+        pq_node_t
+            *a = h,
+            *b = h->next,
+            *rest = b->next;
+        a->next = b->next = NULL;
+        return heap_merge(heap_merge(a, b), two_pass_merge(rest));
+    }
+}
+
+heap_t heap_pop(heap_t h) {
+    return two_pass_merge(h->down);
+}