【leetcode】1680. Concatenation of Consecutive Binary Numbers

题目如下：

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

解题思路：直接计算吧，能AC。

代码如下：

class Solution(object):
    def concatenatedBinary(self, n):
        """
        :type n: int
        :rtype: int
        """
        binStr = ''
        for i in range(1,n+1):
            binStr += bin(i)[2:]
        return int(binStr,2) % (10**9 + 7)