杂七杂八的整理

qsort：

#include <stdio.h>
#include <stdlib.h>

void Print(int num[], int len){
	for(int i = 0; i < len; i ++){
		printf("%d ", num[i]);
	}
	printf("\n");
}

int cmp_up(const void *a, const void *b){ <span style="font-family: Arial, Helvetica, sans-serif;">//记住格式</span>

	return *(int *)a - *(int *)b;
}
int cmp_down(const void *a, const void *b){
	return *(int *)b - *(int *)a;
}

int main()
{
	int num[10] = {39, 8, 2, 7, 16, 11, 23, 9, 20, 33};
	printf("Before Qsort: \n");
	Print(num, 10);
	
	qsort(num, 10, sizeof(int), cmp_up); //记住格式
	printf("After Qsort(up): \n");
	Print(num, 10);

	qsort(num, 10, sizeof(int), cmp_down);	
	printf("After Qsort(down): \n");
	Print(num, 10);
	
	return 0;
}

子集生成：

#include <stdio.h>
int n, vis[10] = {0};
void dfs(int i)
{
    int j;
    if(i == n+1)
    {
        for(j = 1 ; j <= n ; j++)
        {
            if(vis[j])
                printf("%d ", j);
        }
        printf("\n");
        return;
    }
    vis[i] = 0;
    dfs(i+1);
    vis[i] = 1;
    dfs(i+1);
}
int main()
{
    scanf("%d", &n);
    dfs(1);
    return 0;
}