# Python map function | Count total set bits in all numbers from 1 to n

Given a positive integer n, count the total number of set bits in binary representation of all numbers from 1 to n.

Examples:

```Input: n = 3
Output:  4
Binary representations are 1, 2 and 3
1, 10 and 11 respectively. Total set
bits are 1 + 1 + 2 = 4.

Input: n = 6
Output: 9

Input: n = 7
Output: 12

Input: n = 8
Output: 13
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

We have existing solution for this problem please refer Count total set bits in all numbers from 1 to n link. We can solve this problem in python using map() function. Approach is very simple,

1. Write a function which first converts number into binary using bin(num) function and returns count of set bits in it.
2. Map user defined function on list of numbers from 1 to n and we will get list of individual count of set bits in each number.
3. Sum up count of all set bits.

 `# Function to Count total set bits in all numbers ` `# from 1 to n ` ` `  `# user defined function ` `def` `countSetBit(num): ` ` `  `     ``# convert decimal value into binary and ` `     ``# count all 1's in it ` `     ``binary ``=` `bin``(num) ` ` `  `     ``return` `len``([ch ``for` `ch ``in` `binary ``if` `ch``=``=``'1'``]) ` ` `  `# function which count set bits in each number ` `def` `countSetBitAll(``input``): ` `     `  `    ``# map count function on each number ` `    ``print` `(``sum``(``map``(countSetBit,``input``))) ` ` `  `# Driver program ` `if` `__name__ ``=``=` `"__main__"``: ` `    ``n ``=` `8` `    ``input``=``[] ` `    ``for` `i ``in` `range``(``1``,n``+``1``): ` `         ``input``.append(i) ` `    ``countSetBitAll(``input``) `

Output:

```13
```

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