ZOJ 2061 Buy the Ticket

典型的高精度题，本着“和平共处五项原则”，我抄了一下ZXPN的代码，不过略加改进，中间也出了点问题，忘了算fac[0]了。

#include<stdio.h>
#include<string.h>
char dp[105][105][500],fac[105][200];
void add(char *s1,char *s2,char *s3)
{//s3 = s1 + s2
    int len1 = strlen(s1);
    int len2 = strlen(s2);
    int a[10000];
    int k = len1 > len2 ? len1 : len2;
    int i,j;
    for(i = 0;i <= k;i++)
        a[i] = 0;
    for(i = len1 - 1,j = k;i >= 0;i--,j--)
    {
        a[j] = s1[i] - '0';
    }
    for(i = len2 - 1,j = k;i >= 0;i--,j--)
    {
        a[j] = a[j] + s2[i] - '0';
        a[j - 1] = a[j - 1] + a[j] / 10;
        a[j] %= 10;
    }
    if(a[j] >= 10)
    {
        a[j - 1] = a[j] / 10;
        a[j] %= 10;
    }
    i = 0;
    if(a[0] == 0)
        i = 1;
    for(j = i;j <= k;j++)
        s3[j - i] = a[j] + '0';
    s3[j - i] = '\0';
}
void mul(char *s1,char *s2,char *s3)
{//s3 = s1 * s2
    int len1 = strlen(s1);
    int len2 = strlen(s2);
    int a[10000];
    int k = len1 + len2 - 1;
    int i,j;
    for(i = 0;i <= k;i++)
        a[i] = 0;
    for(i = len1 - 1;i >= 0;i--)
    {
        for(j = len2 - 1;j >= 0;j--)
        {
            a[i + j + 1] += (s1[i] - '0') * (s2[j] - '0');
            a[i + j] += a[i + j + 1] / 10;
            a[i + j + 1] %= 10;
        }
    }
    if(a[1] >= 10)
    {
        a[0] = a[1] / 10;
        a[1] %= 10;
    }
    i = 0;
    if(a[0] == 0)
        i = 1;
    for(j = i;j <= k;j++)
        s3[j - i] = a[j] + '0';
    s3[j- i] = '\0';
}
void facmul(char *s1,int n,char *s2)
{//s2 = s1 * n
    int l,k,i,j,t,f=0;
    l = strlen(s1);
    k = l + 2;//本题n最大为100
    for(i = 0; i < k; i++)
        s2[i] = 0;
    for(i = l-1,j = k-1; i >= 0; i--,j--)
    {
        t = (s1[i]-'0') * n;
        s2[j] += t % 10;
        s2[j-1] += t / 10;
        if(s2[j] > 9)
            s2[j-1] += s2[j]/10,s2[j] %= 10;
    }
    if(s2[1] > 9)
        s2[0] += s2[1]/10,s2[1] %= 10;
    while(s2[f] == 0)
        f++;
    for(i = 0; i < k-f; i++)
        s2[i] = s2[i+f]+'0';
    s2[k-f] = '\0';
}
int main()
{
    int i,j,a,b,n=1;
    strcpy(fac[0],"1");
    for(i = 1; i <= 100; i++)
        facmul(fac[i-1],i,fac[i]);
    for(i=0;i<=100;i++)
        strcpy(dp[i][0],"1");
    for(i=1;i<=100;i++)
        for(j=1;j<=i;j++)
            if(i==j)
                strcpy(dp[i][j],dp[i][j-1]);
            else
                add(dp[i][j-1],dp[i-1][j],dp[i][j]);
    for(i = 0;i <= 100;i++)
        for(j = 0;j <= i;j++)
        {
            mul(dp[i][j],fac[i],dp[i][j]);
            mul(dp[i][j],fac[j],dp[i][j]);
        }
    while(~scanf("%d%d",&a,&b),a||b)
    {
        printf("Test #%d:\n",n++);
        if(a < b)
            printf("0\n");
        else
            printf("%s\n",dp[a][b]);
    }
    return 0;
}