M1680.连接连续二进制数字

bit manipulation, https://leetcode.cn/problems/concatenation-of-consecutive-binary-numbers/

思路：记录当前数字的二进制长度即可, 用 (i & (i - 1)) == 0 判断 i 是否为二的幂次

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    int concatenatedBinary(int n) {
        int len = 0, ans = 0, mod = 1e9 + 7;
        for (int i = 1; i <= n; i++) {
            if ((i & (i - 1)) == 0) {
                len++;
            }
            ans = ((long long)ans << len | i) % mod;
        }
        return ans;
    }
};

用时10min