C++程序设计:Fast Mod Exponentiation快速模幂
作者:互联网
Bob has encountered a difficult problem, and hope you design an algorithm to calculate pow(a,b) mod 1337, where a is a positive integer, b is a very large positive integer and will be given in the form of an array. For example, pow(2,3) mod 1337 is 8.
#include <iostream>
#include <vector>
using namespace std;
// pricinple: (a*b)%k = (a%k)(b%k)%k
//fast pow
long pow(long x, long n) {
long curr=x,rs=1;
while(n>0) {
rs%=1337;
curr%=1337;
if(n%2) {
rs*=curr;
}
curr*=curr;
n/=2;
}
rs%=1337;
return rs;
}
int dfs(int a, vector<int> b) {
if(b.empty()) {
return 1;
}
int last=b[b.size()-1];
b.pop_back();
return ((pow(a,last)%1337)*(pow(dfs(a,b),10)%1337)%1337);
}
int main() {
int a;
vector<int> b;
string tmp;
cin>>a;
cin>>tmp;
for(int i=0; i<tmp.length(); i++) {
if(tmp[i]>='0' && tmp[i]<='9') {
b.push_back(int(tmp[i]-'0'));
}
}
cout<<dfs(a,b);
return 0;
}
标签:tmp,模幂,curr,Exponentiation,int,pow,1337,Fast,long 来源: https://blog.csdn.net/qq_41112170/article/details/120983638