Why does my program always get WA#1?
I have tried all the tests in the forum, and all of them are correct.
I think there is a very strange mistake in my program.

#include <stdio.h>
#define re(i, n) for (int i=0; i<n; i++)
#define rre(i, n) for (int i=n-1; i>=0; i--)
const int MAXN = 32;
int b, k;
long long c[MAXN][MAXN], res = 0;
void prp(void)
{
     re(i, MAXN) re(j, MAXN) if (i < j) c[i][j] = 0; else if (!j) c[i][j] = 1; else c[i][j] = c[i - 1][j - 1] * i / j;
}
long long xxx(long long v)
{
     int a[MAXN], len = 0;
     long long r0 = 0;
     while (v) {a[len++] = v % b; v /= b;}
     int k0 = k;
     rre(i, len) {
        int x = a[i];
        if (x >= 2) {r0 += c[i + 1][k0]; break;}
        if (x) {r0 += c[i][k0]; k0--;}
     }
     return r0;
}
int main(void)
{
    long long s, t;
    scanf("%lld%lld%d%d", &s, &t, &k, &b);
    prp();
    res = xxx(t + 1) - xxx(s);
    printf("%lld\n", res);
    return 0;
}


Edited by author 04.09.2010 20:07

I know where the mistake is.
If "k0" is less than 0, it must exit.

Now I got AC.

The test is:
1 30 2 2 --> 10

Right! Right! you must book ticket to madhouse, ok?