Train Problem II

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <memory.h>
 4 
 5 using namespace std;
 6 
 7 #define MAX 101
 8 #define BASE 10000
 9 
10 void multiply(int a[], int len, int b) {
11     for(int i=len-1, carry=0; i>=0; i--) {
12         carry += b * a[i];
13         a[i] = carry % BASE;
14         carry /= BASE;
15     }
16 }
17 
18 void divide(int a[], int len, int b) {
19     for(int i=0, div=0; i<len; i++) {
20         div = div * BASE + a[i];
21         a[i] = div / b;
22         div %= b;
23     }
24 }
25 
26 int main()
27 {
28     int i, j, h[101][MAX];
29     memset(h[1], 0, MAX*sizeof(int));
30     for(i=2, h[1][MAX-1]=1; i<=100; i++) {
31         memcpy(h[i], h[i-1], MAX*sizeof(int));
32         multiply(h[i], MAX, 4*i-2);
33         divide(h[i], MAX, i+1);
34     }
35 
36     while(cin >> i && i>=1 && i <= 100) {
37         for(j=0; j<MAX && h[i][j]==0; j++);
38         printf("%d", h[i][j++]);
39         for(; j<MAX; j++)
40             printf("%04d", h[i][j]);
41         cout << endl;
42     }
43     return 0;
44 }