LeetCode in Kotlin
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
Solution
class Solution {
fun concatenatedBinary(n: Int): Int {
// calculate the length of binary string
var length = 0
var sum: Long = 0
for (i in 1..n) {
if (i and i - 1 == 0) {
length++
}
sum = sum shl length
sum += i.toLong()
if (sum > MOD) {
sum %= MOD
}
}
return (sum % MOD).toInt()
}
companion object {
private const val MOD: Long = 1000000007
}
}