HDOJ 1042 N! -- 大数运算

题目地址：http://acm.hdu.edu.cn/showproblem.php?pid=1042

Problem Description

Given an integer N(0 ≤ N ≤ 10000), your task is to calculate N!

 

Input

One N in one line, process to the end of file.

 

Output

For each N, output N! in one line.

 

Sample Input

  
    

     
   1
2
3
  
    

 

Sample Output

  
    

     
   1
2
6
  
    

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

/* 一个数组元素表示 4 个十进制位，即数组是万进制的 */
#define BIG_RADIX 10000
#define RADIX_LEN 4
/* 10000! 有 35660 位 */
#define MAX_LEN (35660/RADIX_LEN + 1)

int x[MAX_LEN + 1];

void Big_Print(){
	int i;
	int start_output = 0;//用于跳过多余的0

	for (i = MAX_LEN; i >= 0; --i){
		if (start_output == 1){//如果多余的0已经跳过，则输出
			printf("%04d", x[i]);
		}
		else if (x[i] > 0){//表示多余的0已经跳过
			printf("%d", x[i]);
			start_output = 1;
		}
	}
	if (start_output == 0)//如果全为0
		printf("0");
}

void Big_Multiple(int y){
	int i;
	int carry = 0;//保存进位
	int tmp;

	for (i = 0; i < MAX_LEN; ++i){
		tmp = x[i] * y + carry;
		x[i] = tmp % BIG_RADIX;
		carry = tmp / BIG_RADIX;
	}
}

void Big_Factorial(int N){
	int i;

	memset(x, 0, sizeof(x));
	x[0] = 1;
	for (i = 2; i <= N; ++i){
		Big_Multiple(i);
	}
}

int main(void){
	int N;

	while (scanf("%d", &N) != EOF){
		Big_Factorial(N);
		Big_Print();
		printf("\n");
	}
}