Merge pull request xtaci#43 from yanzhe-chen/heap-bug-fix

Fix two bugs in heap implementation.

Author: xtaci

Makefile

@@ -13,6 +13,7 @@ LIBS = -lm
 PROGRAMS = m_based_demo \
 integer_demo \
 	insertion_sort_demo \
+shell_sort_demo \
 	radix_sort_demo \
 	shuffle_demo \
 	quick_sort_demo \
@@ -81,6 +82,9 @@ integer_demo: $(SRCDIR)/integer_demo.cpp
 insertion_sort_demo: $(SRCDIR)/insertion_sort_demo.cpp
 $(CPP) $(CFLAGS) -o $@ $^ $(INCLUDEDIR) $(LIBS)
 
+shell_sort_demo: $(SRCDIR)/shell_sort_demo.cpp
+$(CPP) $(CFLAGS) -o $@ $^ $(INCLUDEDIR) $(LIBS)
+
 radix_sort_demo: $(SRCDIR)/radix_sort_demo.cpp
 $(CPP) $(CFLAGS) -o $@ $^ $(INCLUDEDIR) $(LIBS)
 

README.md

@@ -41,6 +41,7 @@
  Bubble sort
  Selection sort
  Insertion sort
+ Shell sort
  Radix sort
  Quick sort
  Merge sort

include/heap.h

@@ -61,7 +61,7 @@ namespace alg {
 public:
 Heap(int max) {
 m_size = 0;
-m_max = max+1;
+m_max = max;
 m_heap = new elem[m_max];
 };
 
@@ -101,7 +101,7 @@ namespace alg {
 inline void clear() { m_size = 0; }
 
 bool contains(const T & data) {
-for(int i=1;i<=m_size;i++) {
+for(int i=0;i<m_size;i++) {
 if(m_heap[i].data== data) return true;
 }
 return false;
@@ -166,7 +166,7 @@ namespace alg {
 }
 
 int j = j1;
-int j2 = j1+1; // left child
+int j2 = j1+1; // right child
 if (j2 < n && !less(j1,j2)) {
 j = j2; // choose the minium one.
 }

include/shell_sort.h

@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * DANIEL'S ALGORITHM IMPLEMENTAIONS
+ *
+ * /\ | _ _ ._ o _|_ |_ ._ _ _ 
+ * /--\ | (_| (_) | | |_ | | | | | _> 
+ * _| 
+ * 
+ * SHELL SORT 
+ *
+ * 1. sort array in O(n^(3/2)) time.
+ * 
+ * https://en.wikipedia.org/wiki/Shellsort
+ *
+ ******************************************************************************/
+
+#ifndef __SHELL_SORT_H__
+#define __SHELL_SORT_H__
+
+namespace alg {
+/**
+ * shell sort an array
+ */
+template<typename T>
+static void shell_sort(T *array, int len) {
+ int h = 1;
+ while (h < len / 3) {
+ h = 3 * h + 1; // 1, 4, 13, 40, 121, ...
+ }
+ while (h >= 1) {
+ for (int i = h; i < len; i++) {
+ int cur = array[i];
+ int j = i - h;
+ while (j >= 0 && array[j] > cur) {
+ array[j + h] = array[j];
+ j = j - h;
+ }
+ array[j + h] = cur;
+ }
+ h = h / 3;
+ }
+}
+}
+
+#endif //

src/shell_sort_demo.cpp

@@ -0,0 +1,32 @@
+#include <stdio.h> 
+#include <stdlib.h> 
+#include <time.h>
+
+#include "generic.h"
+#include "shell_sort.h"
+
+using namespace alg;
+
+int main()
+{
+const int MAX_ELEMENTS = 10;
+int list[MAX_ELEMENTS];
+
+int i = 0;
+
+srand(time(NULL));
+// generate random numbers and fill them to the list
+for(i = 0; i < MAX_ELEMENTS; i++ ){
+list[i] = rand()%100;
+}
+printf("The list before sorting is:\n");
+printlist(list,MAX_ELEMENTS);
+
+// sort the list using shell sort
+shell_sort<int>(&list[0],MAX_ELEMENTS); 
+
+// print the result
+printf("The list after sorting using shell sort algorithm:\n");
+printlist(list,MAX_ELEMENTS);
+return 0;
+}