1009. Complement of Base 10 Integer 

Description

The complement of an integer is the integer you get when you flip all the 0's to 1's and all the 1's to 0's in its binary representation.

For example, The integer 5 is "101" in binary and its complement is "010" which is the integer 2.

Given an integer n, return its complement.

Example 1:

Input: n = 5
Output: 2
Explanation: 5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.

Example 2:

Input: n = 7
Output: 0
Explanation: 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.

Example 3:

Input: n = 10
Output: 5
Explanation: 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.

Constraints:

0 <= n < 10⁹

Note: This question is the same as 476: https://leetcode.com/problems/number-complement/

Solutions

Solution 1: Bit Manipulation

First, we check if $n$ is $0$. If it is, we return $1$.

Next, we define two variables $\textit{ans}$ and $i$, both initialized to $0$. Then we iterate through $n$. In each iteration, we set the $i$-th bit of $\textit{ans}$ to the inverse of the $i$-th bit of $n$, increment $i$ by $1$, and right shift $n$ by $1$.

Finally, we return $\textit{ans}$.

The time complexity is $O(\log n)$, where $n$ is the given decimal number. The space complexity is $O(1)$.

Python3

class Solution:
    def bitwiseComplement(self, n: int) -> int:
        if n == 0:
            return 1
        ans = i = 0
        while n:
            ans |= ((n & 1 ^ 1) << i)
            i += 1
            n >>= 1
        return ans

Java

class Solution {
    public int bitwiseComplement(int n) {
        if (n == 0) {
            return 1;
        }
        int ans = 0, i = 0;
        while (n != 0) {
            ans |= (n & 1 ^ 1) << (i++);
            n >>= 1;
        }
        return ans;
    }
}

C++

class Solution {
public:
    int bitwiseComplement(int n) {
        if (n == 0) {
            return 1;
        }
        int ans = 0, i = 0;
        while (n != 0) {
            ans |= (n & 1 ^ 1) << (i++);
            n >>= 1;
        }
        return ans;
    }
};

Go

func bitwiseComplement(n int) (ans int) {
	if n == 0 {
		return 1
	}
	for i := 0; n != 0; n >>= 1 {
		ans |= (n&1 ^ 1) << i
		i++
	}
	return
}

TypeScript

function bitwiseComplement(n: number): number {
    if (n === 0) {
        return 1;
    }
    let ans = 0;
    for (let i = 0; n; n >>= 1) {
        ans |= ((n & 1) ^ 1) << i++;
    }
    return ans;
}

Rust

impl Solution {
    pub fn bitwise_complement(mut n: i32) -> i32 {
        if n == 0 {
            return 1;
        }
        let mut ans = 0;
        let mut i = 0;
        while n != 0 {
            ans |= ((n & 1) ^ 1) << i;
            n >>= 1;
            i += 1;
        }
        ans
    }
}