Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Find position of the given number among the numbers made of 4 and 7 in C++
In this problem we are given a number N. Our task is to Find position of the given number among the numbers made of 4 and 7. The series consisting of 4 and 7 only is 4, 7, 44, 47, 74, 77, 444….
Let’s take an example to understand the problem,
Input
N = 5
Output
74
Explanation
Series upto 5 terms is 4, 7, 44, 47, 74…
Solution Approach
A simple solution to the problem is based on finding the pattern in the series.
Here, every even position contains 7 in the end.
And every odd position contains 4 in the end.
So, we can find the series by going digit by digit and finding the position based on the current digit.
If the current digit is 4, the position will be updated as position = (position*2) + 1.
If the current digit is 7, the position will be updated as position = (position*2) + 2.
Program to illustrate the working of our solution,
Example
#include <iostream>
using namespace std;
int findNumPosition(string num){
int i = 0, position = 0;
while (num[i] != '\0') {
position *= 2;
if(num[i] == '4')
position += 1;
else
position += 2;
i++;
}
return position;
}
int main() {
string num = "74774";
cout<<"The position of the number in the series is "<<findNumPosition(num);
return 0;
}Output
The position of the number in the series is 53
282 Views
