【算法】二分查找

 1 // BinarySearch.cpp : Defines the entry point for the console application.
 2 
 3 #include "stdafx.h"
 4 #include <iostream>
 5 
 6 using namespace std;
 7 
 8 //compare function
 9 int compare(const void *val1, const void *val2)
10 {
11     int iVal1 = *(int*)val1;
12     int iVal2 = *(int*)val2;
13 
14     cout << "Compare: " << iVal1 << ", " << iVal2 << endl;
15 
16     if (iVal1 > iVal2)
17     {
18         return 1;
19     }
20     else if (iVal1 == iVal2)
21     {
22         return 0;
23     }
24     else
25     {
26         return -1;
27     }
28 }
29 
30 //nel: num of element, width: every element size
31 void *bsearch(const void *key, const void *base, size_t nel, size_t width, int (*compar)(const void*, const void *))
32 {
33     int pos = nel / 2;
34 
35     cout << "Position: " << pos << endl;
36 
37     int result = (*compar)(key, (int *)base + pos);
38 
39     if (pos == 0)
40     {
41         return result == 0 ? (void *)base : NULL;
42     }
43 
44     if (result > 0)
45     {
46         return bsearch(key, (int *)base + pos + 1, pos, width, compar);
47     }
48     else if (result == 0)
49     {
50         return (void *)base;
51     }
52     else
53     {
54         return bsearch(key, base, pos, width, compar);
55     }
56 }
57 
58 int _tmain(int argc, _TCHAR* argv[])
59 {
60     int array[] = { 1, 3, 5, 6, 11, 13, 17, 29, 44, 66, 79, 99, 111 };
61     int arrayNum = sizeof(array) / sizeof(*array);
62     cout << "Array Element Num: " << arrayNum << endl;
63     
64     int searchVal = 13;
65     cout << "Search Value: " << searchVal << endl;
66 
67     int *result = (int *)bsearch(&searchVal, array, arrayNum, sizeof(*array), compare);
68     
69     cout << "Result: " << (result == NULL ? "Not Found" : "Found") << endl;
70     
71     system("pause");
72     return 0;
73 }