1680. Concatenation of Consecutive Binary Numbers

Problem

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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 10$^9$ + 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 <= 10$^5$

Solution

/**
 * @param {number} n
 * @return {number}
 */
 var concatenatedBinary = function(n) {
  let num = ""
  let result = 0
    for (let i = 1; i <= n; i++) {
      num = result.toString(2)
      num += i.toString(2)
      result = parseInt(num, 2) % 1000000007
    }

    return result
  }