2016 Update

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

@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+    int priority;
+    char *data;
+} node_t;
+
+typedef struct {
+    node_t *nodes;
+    int len;
+    int size;
+} heap_t;
+
+void push (heap_t *h, int priority, char *data) {
+    if (h->len + 1 >= h->size) {
+        h->size = h->size ? h->size * 2 : 4;
+        h->nodes = (node_t *)realloc(h->nodes, h->size * sizeof (node_t));
+    }
+    int i = h->len + 1;
+    int j = i / 2;
+    while (i > 1 && h->nodes[j].priority > priority) {
+        h->nodes[i] = h->nodes[j];
+        i = j;
+        j = j / 2;
+    }
+    h->nodes[i].priority = priority;
+    h->nodes[i].data = data;
+    h->len++;
+}
+
+char *pop (heap_t *h) {
+    int i, j, k;
+    if (!h->len) {
+        return NULL;
+    }
+    char *data = h->nodes[1].data;
+    h->nodes[1] = h->nodes[h->len];
+    h->len--;
+    i = 1;
+    while (1) {
+        k = i;
+        j = 2 * i;
+        if (j <= h->len && h->nodes[j].priority < h->nodes[k].priority) {
+            k = j;
+        }
+        if (j + 1 <= h->len && h->nodes[j + 1].priority < h->nodes[k].priority) {
+            k = j + 1;
+        }
+        if (k == i) {
+            break;
+        }
+        h->nodes[i] = h->nodes[k];
+        i = k;
+    }
+    h->nodes[i] = h->nodes[h->len + 1];
+    return data;
+}
+
+int main () {
+    heap_t *h = (heap_t *)calloc(1, sizeof (heap_t));
+    push(h, 3, "Clear drains");
+    push(h, 4, "Feed cat");
+    push(h, 5, "Make tea");
+    push(h, 1, "Solve RC tasks");
+    push(h, 2, "Tax return");
+    int i;
+    for (i = 0; i < 5; i++) {
+        printf("%s\n", pop(h));
+    }
+    return 0;
+}