From 621e895b19d908f835f9627d441b8197c203e9be Mon Sep 17 00:00:00 2001
From: Valentin Gehrke <madmaurice@zom.bi>
Date: Thu, 11 Feb 2016 15:04:21 +0100
Subject: [PATCH] EPA: Heapsort

---
 heapsort.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 heapsort.c

diff --git a/heapsort.c b/heapsort.c
new file mode 100644
index 0000000..4b88d83
--- /dev/null
+++ b/heapsort.c
@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <assert.h>
+#include <time.h>
+
+void swap(int* data, size_t i, size_t j) {
+    int tmp = data[i];
+    data[i] = data[j];
+    data[j] = tmp;
+}
+
+void siftdown(int* data, size_t n, size_t i) {
+    while(2*i+1<n) {
+        if(2*i+2>=n) {
+            if(data[i] < data[2*i+1]) {
+                swap(data, i, 2*i+1);
+                i = 2*i+1;
+            } else {
+                break;
+            }
+        } else {
+            if(data[i] < data[2*i+1] && data[2*i+1] > data[2*i+2]) {
+                swap(data, i, 2*i+1);
+                i = 2*i+1;
+            } else if(data[i] < data[2*i+2]) {
+                swap(data, i, 2*i+2);
+                i = 2*i+2;
+            } else {
+                break;
+            }
+        }
+    }
+}
+
+void heapcreate(int* data, size_t n) {
+    for(int i = (n-2)/2; i >= 0; i--) {
+        siftdown(data, n, i);
+    }
+}
+
+void heapsort(int* data, size_t n) {
+    heapcreate(data, n);
+    for(size_t i = n-1; i > 0; i--) {
+        swap(data, 0, i);
+        siftdown(data, i, 0);
+    }
+}
+
+int main( int argc, char *argv[] ) {
+
+    int n = 1000;
+    if(argc > 1) n = atoi(argv[1]);
+    srand(time(NULL));
+    int* data = malloc(sizeof(int)*n);
+    for(size_t i = 0; i < n; i++) {
+        data[i] = rand();
+    }
+    heapsort(data,n);
+    int prev = data[0];
+    for(size_t i = 1; i < n; i++) {
+        assert(prev <= data[i]);
+        prev = data[i];
+    }
+	return 0;
+}