remove choose_pivot function from generic.h

adding a more generic interval RANDOM() function

Author: xtaci

include/generic.h

@@ -23,6 +23,9 @@
 #define Max(a, b) ( (a > b) ? a : b )
 #define Min(a, b) ( (a < b) ? a : b )
 
+#define RANDOM_INIT()	srand(time(NULL))
+#define RANDOM(L, R)	(L + rand() % ((R) - (L))) // gen a random integer in [L, R]
+
 namespace alg 
 {
 	/**
@@ -48,16 +51,6 @@ namespace alg
 		printf("\n");
 	}
 
-	/**
-	 * select a random number between i and j
-	 */
-	static inline int choose_pivot(int i,int j)
-	{
-		assert(j>=i);
-		int length = j - i;
-		return i+(rand()%length);
-	}
-
 	/**
 	 * pass in array with *len
 	 * return new length

include/quick_sort.h

@@ -28,7 +28,7 @@ namespace alg
 	template<typename T>
 	static int __partition(T list[],int begin, int end)
 	{
-		int pivot_idx = choose_pivot(begin,end);
+		int pivot_idx = RANDOM(begin,end);
 		T pivot = list[pivot_idx];
 		swap(list[begin], list[pivot_idx]);
 

include/random_select.h

@@ -18,6 +18,8 @@
 #ifndef __RANDOM_SELECT_H__
 #define __RANDOM_SELECT_H__
 
+#include <generic.h> 
+
 namespace alg
 {
 	/**
@@ -26,7 +28,7 @@ namespace alg
 	template<typename T>
 	static int __partition(T list[],int begin, int end)
 	{
-		int pivot_idx = choose_pivot(begin,end);
+		int pivot_idx = RANDOM(begin,end);
 		T pivot = list[pivot_idx];
 		swap(list[begin],list[pivot_idx]);
 

src/quick_sort_demo.cpp

@@ -7,6 +7,7 @@
 
 int main()
 {
+	RANDOM_INIT();
 	using namespace alg;
 	const int MAX_ELEMENTS = 10;
 	int list[MAX_ELEMENTS];

src/random_select_demo.cpp

@@ -7,6 +7,7 @@
 
 int main()
 {
+	RANDOM_INIT();
 	using namespace alg;
 	const int MAX_ELEMENTS = 10;
 	int list[MAX_ELEMENTS];
@@ -18,7 +19,7 @@ int main()
 		list[i] = rand()%100; 
 	}
 
-	printf("The list before sorting is:\n");
+	printf("The list is:\n");
 	printlist(list,MAX_ELEMENTS);
 
 	// random-select k-th element
@@ -27,7 +28,7 @@ int main()
 	int result = random_select(list,0,MAX_ELEMENTS-1,k);
 
 	// print the result
-	printf("the %dth smallest number is %d:\n", k, list[result]);
+	printf("random select the %dth smallest number %d:\n", k, list[result]);
 
 	return 0;
 }