USACO: Factorials

最新推荐文章于 2022-02-25 19:38:17 发布

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本文介绍了一个用于计算阶乘尾部非零数字的C++程序设计方法。该程序能够接收一个正整数输入，并输出其阶乘结果中从右往左第一个非零数字。文章提供了一种有效避免大量数值运算导致溢出的方法。

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)

这题瞎蒙的，开始保留最后两个非零位计算，结果好像在645的地方错了，所以又改了保留三个，就顺利通过了

/* ID: geterns1 PROG: fact4 LANG: C++ */ #include <iostream> #include <fstream> #include <cstdio> #include <cmath> #include <cstdlib> #include <cstring> #include <algorithm> using namespace std; int main(){ freopen("fact4.in", "r", stdin); freopen("fact4.out", "w", stdout); int lim, fac = 1; scanf("%d", &lim); for (int i = 1; i <= lim; i ++){ fac *= i; while (fac % 10 == 0) fac /= 10; fac %= 1000; } printf("%d/n", fac % 10); fclose(stdin); fclose(stdout); return 0; }