Hà Phan（河）

Problem

Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Example 1:

``````Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.
``````

Example 2:

``````Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.
``````

Note:

Solution

Bitwising

Flip every bit from right to left

``````class Solution {
func findComplement(_ num: Int) -> Int {
if num == 0 { return 1 }
var it = num
var res = 0

while it > 0 {
if it & 1 == 0 {
}

it >>= 1
}

return res
}
}
``````

Substraction

complement + num + 1 = 2^n (n is bit length of num)
example: 101 + 010 + 1 = 1000

``````class Solution {
func findComplement(_ num: Int) -> Int {
var higher = 1
while higher <= num {
higher <<= 1
}
return higher - num - 1
}
}
``````