1680. Concatenation of Consecutive Binary Numbers

Medium

Given an integer n, return the decimal value of the binary string formed by concatenating the binary representations of 1 to n in order, modulo 109 + 7.

Example 1:

Input: n = 1
Output:
 1
Explanation: 
"1" in binary corresponds to the decimal value 1. 

Example 2:

Input: n = 3
Output:
 27
Explanation: 
In binary, 1, 2, and 3 corresponds to "1", "10", and "11".
After concatenating them, we have "11011", which corresponds to the decimal value 27.

Example 3:

Input: n = 12
Output:
 505379714
Explanation
: The concatenation results in "1101110010111011110001001101010111100".
The decimal value of that is 118505380540.
After modulo 109 + 7, the result is 505379714.

Constraints:

• 1 <= n <= 105

class Solution:
    def concatenatedBinary(self, n: int) -> int:
        result = ""
        MOD = 10**9+7
        for num in range(1, n+1):
            b = bin(num)[2:]
            result += b
        return int(result, 2) % MOD