10474 Where is the Marble?

排序，检索；

使用 bsearch 的 cmp 不能只返回 -1 或 1 （可能是要用差进行比较）；

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

# define N 10005

int n, q, a[N], f[N];

int cmp(const void *x, const void *y){return ( *(int*)x - *(int*)y );}

int main()
{
    int i, cnt, x;
        
    cnt = 0;
    while (1)
    {
        scanf("%d%d", &n, &q);
        if (!n && !q) break;
        
        ++cnt;
        printf("CASE# %d:\n", cnt);
        for (i = 0; i < n; ++i) scanf("%d", &a[i]);
        
        qsort(a, n, sizeof(a[0]), cmp);
        
        memset(f, 0, sizeof(f));
        for (i = 0; i < n; ++i) if (!f[a[i]]) f[a[i]] = i+1;
        for (i = 0; i < q; ++i)    
        {
            scanf("%d", &x);
            if (!f[x]) printf("%d not found\n", x);
            else printf("%d found at %d\n", x, f[x]);
        }
    }
    
    return 0;
}

使用 bsearch ：

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

# define N 10005

int n, q, f[N], h[N];

int cmp(const void *x, const void *y) {return *(int*)x - *(int*)y;}

int main()
{
    int i, x, *p, cnt;
        
    cnt = 0;
    while (1)
    {
        scanf("%d%d", &n, &q);
        if (!n && !q) break;
        
        ++cnt;
        printf("CASE# %d:\n", cnt);
        for (i = 0; i < n; ++i) scanf("%d", &f[i]);
        
        qsort(f, n, sizeof(f[0]), cmp);
        
        for (i = 0; i < q; ++i)
        {
            scanf("%d", &x);
            p = (int*)bsearch(&x, f, n, sizeof(f[0]), cmp);
            if (p == NULL) printf("%d not found\n", x);
            else
            {
                while (*(--p) == x) ;
                printf("%d found at %d\n", x, p-f+2);
            }
        }
    }
    
    return 0;
}