有1,2,3,4,5四个数，能组成多少个互不相同且无重复的三位数?

Question

最近C语言老师布置了一道题:有1,2,3,4,5四个数，能组成多少个互不相同且无重复的三位数?请用至少三种方法。

Answer 1

#include
#include
char array[] = "1234";
#define N 4
#define M 3
int queue[N] = {0};
int top = 0;
int flag[N] = {0};
void perm(int s, int n)
{
int i;
if (s > n)
{

return;
}
if (s == n)
{
for (i = 0; i < n; i++)
{
printf("%c", queue[i]);
}
printf("\t");
return ;
}
for (i = 0; i < n; i++)
{
if (flag[i] == 0)
{
flag[i] = 1;
queue[s] = array[i];
perm(s+1, n);
flag[i] = 0;
}
}
}

void comb(int s, int n, int m)
{
int i;
if (s > n)
return ;
if (top == m)
{
for (i = 0; i < m; i++)
{
printf("%c", queue[i]);
}
printf("\t");
return ;
}
queue[top++] = array[s];
comb(s+1, n, m);
top--;
comb(s+1, n, m);
}
int main()
{
printf("\nperm():\n");
perm(0, N);
printf("\ncombination():\n");
comb(0, N, M);
printf("\n");
return 0;
}