UVaLive 7457 Discrete Logarithm Problem (暴力)

Posted 2020-08-09 dwtfukgv

题意：求一个x使得 a^x%p = b p为素数；

析：从1开始扫一下就好，扫到p-1就可以了，关键是这个题为什么要用文件尾结束，明明说是0，但是不写就WA。。。

代码如下：

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
#include <cmath>
#include <stack>
#define freopenr freopen("in.txt", "r", stdin)
#define freopenw freopen("out.txt", "w", stdout)
using namespace std;
typedef long long LL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const double inf = 0x3f3f3f3f3f3f;
const LL LNF = 0x3f3f3f3f3f3f;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int maxn = 1e3 + 100;
const int mod = 1e9 + 7;
const int dr[] = {-1, 0, 1, 0};
const int dc[] = {0, 1, 0, -1};
const char *Hex[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};
int n, m;
const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
inline int Min(int a, int b){ return a < b ? a : b; }
inline int Max(int a, int b){ return a > b ? a : b; }
inline LL Min(LL a, LL b){ return a < b ? a : b; }
inline LL Max(LL a, LL b){ return a > b ? a : b; }
inline bool is_in(int r, int c){
    return r >= 0 && r < n && c >= 0 && c < m;
}
int solve(int a, int b, int m){
    int x = a;
    for(int i = 1; i < m; ++i){
        if(x == b)  return i;
        x = (x * a) % m;
    }
    return 0;
}

int main(){
    int r, m, a;
    scanf("%d", &m);
    while(scanf("%d", &a) == 1){
        if(!a)  break;
        scanf("%d", &r);
        int ans = solve(a, r%m, m);
        printf("%d\n", ans);
    }
    return 0;
}