Introduction to competitive programming

Problem :

#include<iostream>
using namespace std;
long long phi(long long n) 
{ 
	long  long result = n; 
        for(long  long i=2;i*i <= n;i++) 
        { 
		if (n%i==0) 
		result-=result/i; 
        	while (n%i==0) 
		n/=i; 
        } 
        if (n>1) 
	result-=result/n; 
        return result; 
} 
int main()
{
	long long t,n;
	cin>>t;	
	while(t--)
	{
		cin>>n;
		cout<<phi(n)<<endl;
	}
} 

Problem:

Just find the power of Last disit using Logarithmic exponentiation

Here is the C++ implementation

#include<stdio.h>
long long modexpo(long long a,long long b,long long n)
{
    long long d=1;
    while(b)
    {
        if(b%2)
            d=(d*a)%n;
        b>>=1;
        a=(a*a)%n;
    }
    return d;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        long long a,b;
        scanf("%lld%lld",&a,&b);
        printf("%lld\n",modexpo(a,b,10));
    }
    return 0;
}