Maximize the number by rearranging bits in C++

Problem statement

Given an unsigned number, find the maximum number that could be formed by using the bits of the given unsigned number

If the input number is 8 then its binary representation is−

00000000000000000000000000001000

To maximize it set MSB to 1. Then number becomes 2147483648 whose binary representation is−

10000000000000000000000000000000

Algorithms

1. Count number of set bits in the binary representation of a given number
2. Find a number with n least significant set bits
3. shift the number left by (32 – n)

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
unsigned getMaxNumber(unsigned num){
   int n = __builtin_popcount(num);
   if (n == 32) {
      return num;
   }
   unsigned result = (1 << n) - 1;
   return (result << (32 - n));
}
int main(){
   unsigned n = 8;
   cout << "Maximum number = " << getMaxNumber(n) << endl;
   return 0;
}

Output

When you compile and execute the above program. It generates the following output−

Maximum number = 2147483648