Problem B: Discrete Logging

code

6 年前

时间： 1ms 内存：128M

描述：

Problem B: Discrete Logging

Given a prime P, 2 <= P < 2³¹, an integer B, 2 <= B < P, and an integer N, 2 <= N < P, compute the discrete logarithm of N, base B, modulo P. That is, find an integer L such that
    B^L == N (mod P)
Read several lines of input, each containing P,B,N separated by a space, and for each line print the logarithm on a separate line. If there are several, print the smallest; if there is none, print "no solution".

The solution to this problem requires a well known result in number theory that is probably expected of you for Putnam but not ACM competitions. It is Fermat's theorem that states
   B^(P-1) == 1 (mod P)
for any prime P and some other (fairly rare) numbers known as base-B pseudoprimes. A rarer subset of the base-B pseudoprimes, known as Carmichael numbers, are pseudoprimes for every base between 2 and P-1. A corollary to Fermat's theorem is that for any m
   B^(-m) == B^(P-1-m) (mod P) .

输入：

输出：

示例输入：

5 2 1
5 2 2
5 2 3
5 2 4
5 3 1
5 3 2
5 3 3
5 3 4
5 4 1
5 4 2
5 4 3
5 4 4
12345701 2 1111111
1111111121 65537 1111111111

示例输出：

0
1
3
2
0
3
1
2
0
no solution
no solution
1
9584351
462803587

提示：

参考答案（内存最优[936]）：

#include <stdio.h>
#include <string.h>
#include <map>
#include <malloc.h>
using namespace std;
struct species {
   char s[81];
} buf;

bool operator==(const species &a, const species &b) {
   return !strcmp(a.s, b.s);
}

bool operator<(const species &a, const species &b) {
   return strcmp(a.s, b.s) < 0;
}

map<species,int> cnt;

main(){
   int tot = 0;
   while(gets(buf.s)){
      cnt[buf]++;
      tot++;
   }
   for (map<species,int>::iterator i = cnt.begin(); i!=cnt.end(); *i++) {
      printf("%s %0.4lf\n",i->first.s, 100.0*i->second/tot);
   }
}

/**************************************************************
	Problem: 1270
	User: zhblue
	Language: C++
	Result: Compile Error
****************************************************************/

参考答案（时间最优[1160]）：

#include <stdio.h>
#include <string.h>
#include <map>
#include <malloc.h>
using namespace std;
struct species {
   char s[81];
} buf;

bool operator==(const species &a, const species &b) {
   return !strcmp(a.s, b.s);
}

bool operator<(const species &a, const species &b) {
   return strcmp(a.s, b.s) < 0;
}

map<species,int> cnt;

main(){
   int tot = 0;
   while(gets(buf.s)){
      cnt[buf]++;
      tot++;
   }
   for (map<species,int>::iterator i = cnt.begin(); i!=cnt.end(); *i++) {
      printf("%s %0.4lf\n",i->first.s, 100.0*i->second/tot);
   }
}

/**************************************************************
	Problem: 1270
	User: zhblue
	Language: C++
	Result: Compile Error
****************************************************************/

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