【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 = ;
         y = ;
     } 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 != )
         return -;

     return x%n== ? 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 == -) {
             puts ("Not Exist");
         } else {
             printf("%lld\n", ans);
         }
     }

     #ifndef ONLINE_JUDGE
         printf("time = %d.\n", (int)clock());
     #endif

     return ;
 }

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\n" % (t))
         for tt in xrange(t):
             n = randint(1, 1000)
             m = randint(1, 1000)
             fout.write("%d %d\n" % (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_prj\hdoj\data.out"
     desFileName = "F:\workspace\cpp_hdoj\data.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_prj\hdoj\data.in"
     desFileName = "F:\workspace\cpp_hdoj\data.in"
     GenData(srcFileName)
     MovData(srcFileName, desFileName)