1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <stdbool.h>
 4 
 5 int Combine(const int const arr[], const int n, const int m)
 6 {
 7 #define MAX_COMBINE_M 10
 8 #define MAX_COMBINE_N 10
 9 
10     if (m > MAX_COMBINE_M || n > MAX_COMBINE_N) {
11         printf("OverSize!\n");
12         return 0;
13     }
14     unsigned int i;
15     bool printFlag = false;
16     unsigned int curPos = 0; /* 指示pick数组的当前下标 */
17     unsigned int cnt = 0;
18     unsigned int *pick = (unsigned int *)malloc(sizeof(unsigned int) * m); /* 保存从arr中选取的元素下标 */
19 
20     for (i = 0; i < m; i++) {
21         pick[i] = 0;
22     }
23 
24     while (pick[0] + m <= n + 1) { /* C(m,n)全部组合选取完毕判断条件 */
25         if (printFlag) {
26             for (i = 0; i < m; i++) {
27                 printf("%d ", arr[pick[i] - 1]);
28             }
29             printf("\n");
30             printFlag = false;
31             cnt++;
32         }
33 
34         pick[curPos]++; /* 选取arr中下一个元素, 值为1对应arr数组下标0 */
35         if (pick[curPos] == n + 1) { /* 当前位置无元素可选，回溯 */
36             pick[curPos] = 0;
37             curPos--;
38             continue;
39         }
40 
41         if (curPos < m - 1) { /* 还有剩余位置未选取，选取下一个元素 */
42             curPos++;
43             pick[curPos] = pick[curPos - 1]; /* 防止重复，当前位置的元素选取从上一个位置的元素的开始 */
44             continue;
45         }
46 
47         if (curPos == m - 1) { /* m个元素选取完毕 */
48             printFlag = true;
49         }
50     }
51     free(pick);
52     return cnt;
53 }
54 
55 int main()
56 {
57 #define N  5;
58 #define M  3;
59     int a[] = {0, 1, 2, 3, 4};
60 
61     printf("cnt = %d\n", Combine(a, N, M));
62 
63     return 0;
64 }