、组合问题（从M个不同字符中任取N个字符的所有组合）

void find(char *source, char *result, int n) {
     if(n==1) {
         while(*source)
            printf(”%s%c\n”, result, *source++);
     } else {
         int i, j;
         for(i=0; source[i] != 0; i++);
         for(j=0; result[j] != 0; j++);
         for(; i>=n; i-) {
              result[j] = *source++;
              result[j+1] = ‘\0′;
              find(source, result, n-1);
         }
     }
}
 
int main(int argc, char* argv[]) {
     int const n = 3;
     char *source = “ABCDE”, result[n+1] = {0};
     if(n>0 && strlen(source)>0 && n<=strlen(source))
         find(source, result, 3);
}