USACO SECTION 3.2 Factorials

最新推荐文章于 2021-02-05 11:05:28 发布

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最新推荐文章于 2021-02-05 11:05:28 发布

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分类专栏： USACO 文章标签： integer output file input

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本文介绍了一个用于计算正整数N阶乘尾部第一个非零数字的C语言程序。通过逐步相乘并去除末尾的零，该算法能够有效找出指定数值阶乘后的最右端非零数字。

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Factorials

The factorial of an integer N, written N!, is the product of all the integers from 1 through N inclusive. The factorial quickly becomes very large: 13! is too large to store in a 32-bit integer on most computers, and 70! is too large for most floating-point variables. Your task is to find the rightmost non-zero digit of n!. For example, 5! = 1 * 2 * 3 * 4 * 5 = 120, so the rightmost non-zero digit of 5! is 2. Likewise, 7! = 1 * 2 * 3 * 4 * 5 * 6 * 7 = 5040, so the rightmost non-zero digit of 7! is 4.

PROGRAM NAME: fact4

INPUT FORMAT

A single positive integer N no larger than 4,220.

SAMPLE INPUT (file fact4.in)

OUTPUT FORMAT

A single line containing but a single digit: the right most non-zero digit of N! .

SAMPLE OUTPUT (file fact4.out)

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

int main()
{
	FILE *fin,*fout;
	fin=fopen("fact4.in","r");
	fout=fopen("fact4.out","w");
	int N,sum;
	fscanf(fin,"%d",&N);
	sum=1;
	while(N>1){
		sum*=N;
		while(sum%10==0)
			sum/=10;
		sum%=100000;
		N--;
	}
	sum%=10;
	fprintf(fout,"%d\n",sum);
	
	return 0;
}

一开始蠢了。。居然直接取最后一个的非0位。。