【ZOJ】3609 Modular Inverse

1. 题目描述
求乘法逆元。

2. 基本思路
利用扩展gcd求逆元，模板题目。

3. 代码

/* 3609 */
#include <iostream>
#include <sstream>
#include <string>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
#include <deque>
#include <bitset>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <climits>
#include <cctype>
#include <cassert>
#include <functional>
#include <iterator>
#include <iomanip>
using namespace std;
//#pragma comment(linker,"/STACK:102400000,1024000")

#define sti                set<int>
#define stpii            set<pair<int, int> >
#define mpii            map<int,int>
#define vi                vector<int>
#define pii                pair<int,int>
#define vpii            vector<pair<int,int> >
#define rep(i, a, n)     for (int i=a;i<n;++i)
#define per(i, a, n)     for (int i=n-1;i>=a;--i)
#define clr                clear
#define pb                 push_back
#define mp                 make_pair
#define fir                first
#define sec                second
#define all(x)             (x).begin(),(x).end()
#define SZ(x)             ((int)(x).size())
#define lson            l, mid, rt<<1
#define rson            mid+1, r, rt<<1|1

#define LL long long

void egcd(LL a, LL b, LL& g, LL& x, LL& y) {
    if (!b) {
        g = a;
        x = 1;
        y = 0;
    } else {
        egcd(b, a%b, g, y, x);
        y -= a/b*x;
    }
}

int inv(LL a, LL n) {
    LL g, x, y;
    
    egcd(a, n, g, x, y);
    if (g != 1)
        return -1;
    
    return x%n==0 ? n:(x%n+n)%n;
}

int main() {
    ios::sync_with_stdio(false);
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        freopen("data.out", "w", stdout);
    #endif
    
    int t;
    LL a, m;
    LL ans;
    
    scanf("%d", &t);
    while (t--) {
        scanf("%lld%lld", &a, &m);
        ans = inv(a, m);
        if (ans == -1) {
            puts ("Not Exist");
        } else {
            printf("%lld
", ans);
        }
    }
    
    #ifndef ONLINE_JUDGE
        printf("time = %d.
", (int)clock());
    #endif
    
    return 0;
}

4. 代码生成器

import sys
import string
from random import randint

    
def GenData(fileName):
    with open(fileName, "w") as fout:
        t = 1000
        fout.write("%d
" % (t))
        for tt in xrange(t):
            n = randint(1, 1000)
            m = randint(1, 1000)
            fout.write("%d %d
" % (n, m))
                
        
def MovData(srcFileName, desFileName):
    with open(srcFileName, "r") as fin:
        lines = fin.readlines()
    with open(desFileName, "w") as fout:
        fout.write("".join(lines))

        
def CompData():
    print "comp"
    srcFileName = "F:Qt_prjhdojdata.out"
    desFileName = "F:workspacecpp_hdojdata.out"
    srcLines = []
    desLines = []
    with open(srcFileName, "r") as fin:
        srcLines = fin.readlines()
    with open(desFileName, "r") as fin:
        desLines = fin.readlines()
    n = min(len(srcLines), len(desLines))-1
    for i in xrange(n):
        ans2 = int(desLines[i])
        ans1 = int(srcLines[i])
        if ans1 > ans2:
            print "%d: wrong" % i

            
if __name__ == "__main__":
    srcFileName = "F:Qt_prjhdojdata.in"
    desFileName = "F:workspacecpp_hdojdata.in"
    GenData(srcFileName)
    MovData(srcFileName, desFileName)