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 <= 105struct Solution;
const MOD: i64 = 1_000_000_007;
impl Solution {
fn concatenated_binary(n: i32) -> i32 {
let mut res = 0;
let mut stack: Vec<i64> = vec![];
for i in 1..=n {
let mut j = i;
while j > 0 {
stack.push((j % 2) as i64);
j >>= 1;
}
while let Some(top) = stack.pop() {
res <<= 1;
res += top;
}
res %= MOD;
}
res as i32
}
}
#[test]
fn test() {
let n = 1;
let res = 1;
assert_eq!(Solution::concatenated_binary(n), res);
let n = 3;
let res = 27;
assert_eq!(Solution::concatenated_binary(n), res);
let n = 12;
let res = 505379714;
assert_eq!(Solution::concatenated_binary(n), res);
}