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HDU1066 Last non-zero Digit in N!

2024-07-28 02:40:56   215人阅读

Last non-zero Digit in N!

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 6276    Accepted Submission(s): 1556


Problem Description
The expression N!, read as "N factorial," denotes the product of the first N positive integers, where N is nonnegative. So, for example,
N N!
0 1
1 1
2 2
3 6
4 24
5 120
10 3628800

For this problem, you are to write a program that can compute the last non-zero digit of the factorial for N. For example, if your program is asked to compute the last nonzero digit of 5!, your program should produce "2" because 5! = 120, and 2 is the last nonzero digit of 120.
 

Input
Input to the program is a series of nonnegative integers, each on its own line with no other letters, digits or spaces. For each integer N, you should read the value and compute the last nonzero digit of N!.
 

Output
For each integer input, the program should print exactly one line of output containing the single last non-zero digit of N!.
 

Sample Input
1 
2 
26 
125 
3125 
9999
 

Sample Output
1
2
4
8
2
8
 

Source
South Central USA 1997 

求N!的最后一个非零数字，套模板。

#include <string.h>
#include <stdio.h>
#define MAXN 10000
int a[MAXN];
char str[MAXN];
const int mod[20]={1,1,2,6,4,2,2,4,2,8,4,
					4,8,4,6,8,8,6,8,2};
int lastdigit(char *buf){
	int len = strlen(buf), i, c, ret = 1;
	if(len == 1) return mod[buf[0] - '0'];
	for(i = 0; i < len; ++i) a[i] = buf[len-1-i] - '0';
	for(; len; len -= !a[len-1]){
		ret = ret * mod[a[1]%2*10+a[0]] % 5;
		for(c = 0,i = len - 1;i >= 0; --i)
			c = c * 10 + a[i], a[i] = c / 5, c %= 5;
	}
	return ret + ret % 2 * 5;
}
int main(){
	while(scanf("%s", str) == 1){
		printf("%d\n", lastdigit(str));
	}
	return 0;
}


HDU1066 Last non-zero Digit in N!


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