Description

Submission

class Solution {
public:
    int concatenatedBinary(int n) {
        long long res = 1;
        long long M = 1e9 + 7;
        for(int i = 2; i <= n; ++i) {
            int pos = log(i) / log(2)+1;
            res = ((res << pos) % M + i) % M;
        }

        return res;
    }
};

// n = 1: 1
// n = 2: 1 10
// n = 3: 110 11

// res[n] = ()res[n-1]*2^l+n)M