Third last digit in 5^N for given N
Last Updated :
16 Dec, 2022
Given a positive integer N, The task is to find the value of the 3rd digit from the last (right-most) of 5N.
Examples:
Input : N = 6
Output : 6
Explanation : Value of 56 = 15625.
Input : N = 3
Output : 1
Explanation : Value of 53 = 125.
Approach: Before moving to the actual approach, some facts regarding number theory are listed below as:
- 53 is the smallest 3-digit number which is a power of 5.
- As 125 * 5 = 625, this concludes that multiple of numbers (ending with 125) with 5 always construct 625 as of the last three digits of the result.
- Again as, 625 * 5 = 3125, this concludes that multiple numbers (ending with 625) with 5 always construct 125 as the last three digits of the result.
Hence, the final general solution is :
Case 1: if n < 3, answer = 0.
Case 2: if n >= 3 and is even, answer = 6.
Case 3: if n >= 3 and is odd, answer = 1.
Below is the implementation of the above approach:
C++
#include <bits/stdc++.h>
using namespace std;
int findThirdDigit( int n)
{
if (n < 3)
return 0;
return n & 1 ? 1 : 6;
}
int main()
{
int n = 7;
cout << findThirdDigit(n);
return 0;
}
|
Java
import java.io.*;
class GFG
{
static int findThirdDigit( int n)
{
if (n < 3 )
return 0 ;
return (n & 1 ) > 0 ? 1 : 6 ;
}
public static void main(String args[])
{
int n = 7 ;
System.out.println(findThirdDigit(n));
}
}
|
Python3
def findThirdDigit(n):
if n < 3 :
return 0
return 1 if n and 1 else 6
n = 7
print (findThirdDigit(n))
|
C#
using System;
class GFG
{
static int findThirdDigit( int n)
{
if (n < 3)
return 0;
return (n & 1)>0 ? 1 : 6;
}
static void Main()
{
int n = 7;
Console.WriteLine(findThirdDigit(n));
}
}
|
PHP
<?php
function findThirdDigit( $n )
{
if ( $n < 3)
return 0;
return $n & 1 ? 1 : 6;
}
$n = 7;
echo findThirdDigit( $n );
?>
|
Javascript
<script>
function findThirdDigit(n)
{
if (n < 3)
return 0;
return n & 1 ? 1 : 6;
}
var n = 7;
document.write( findThirdDigit(n));
</script>
|
Time Complexity: O(1)
Auxiliary Space: O(1), since no extra space has been taken.
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