CODEWITHSUNDEEP
c++math
Sarin Nanda
Sarin Nanda

Reputation: 35

Find the last digit of a number raised to a certain power

I am trying to find the unit digit of a number raised to a certain power, using the simplest method. I know about modular exponentiation. I am trying to implement something similar to How to find the units digit of a certain power in a simplest way, but my code is showing the wrong answer for certain test cases in SPOJ. Here is the link to the question in SPOJ: http://www.spoj.com/problems/LASTDIG/

#include<iostream>
using namespace std;

int main() {
    int a2[] = {6, 2, 4, 8},
        a3[] = {1, 3, 9, 7},
        a4[] = {6, 4},
        a7[] = {1, 7, 9, 3},
        a8[] = {6, 8, 4, 2},
        a9[] = {1, 9},
        t;
    long long int b1, b2;

    cin >> t;

    while (t--) {
        cin >> b1 >> b2;
        b1 = b1 % 10;
        if (b2 == 0)
            cout << 1 << endl;
        else if (b1 == 0)
            cout << 0 << endl;
        else if (b2 == 1 || b1 == 5 || b1 == 6)
            cout << b1 << endl;
        else if (b1 == 2)
            cout << a2[b2 % 4] << endl;
        else if (b1 == 3)
            cout << a3[b2 % 4] << endl;
        else if (b1 == 4)
            cout << a4[b2 % 2] << endl;
        else if (b1 == 7)
            cout << a7[b2 % 4] << endl;
        else if (b1 == 8)
            cout << a8[b2 % 4] << endl;
        else if (b1 == 9)
            cout << a9[b2 % 2] << endl;
    }
    return 0;
}

Upvotes: 0

Views: 369

Answers (1)

D&#233;j&#224; vu
D&#233;j&#224; vu

Reputation: 28830

First

a7[]={1,7,0,3}
         ^^^

zero should be 9

a7[]={1,7,9,3}

And a9

a9[]={9,1}
      ^^^

should be reverse

a9[]={1,9}

Upvotes: 1

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