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476. Number Complement (Easy)

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 num, return its complement.

 

Example 1:

Input: num = 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: num = 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.

 

Constraints:

• 1 <= num < 231

 

Note: This question is the same as 1009: https://leetcode.com/problems/complement-of-base-10-integer/

Companies:
Apple

Related Topics:
Bit Manipulation

Solution 1.

For example:

num          = 00000101
mask         = 11111000
~mask & ~num = 00000010

// OJ: https://leetcode.com/problems/number-complement/
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class Solution {
public:
    int findComplement(int num) {
        unsigned mask = ~0;
        while (num & mask) mask <<= 1;
        return ~mask & ~num;
    }
};

Solution 2.

// OJ: https://leetcode.com/problems/number-complement/
// Author: github.com/lzl124631x
// Time: O(1)
// Space: O(1)
class Solution {
public:
    int findComplement(int n) {
        return (unsigned)~0 >> __builtin_clz(n) ^ n;
    }
};

For example:

n                                    = 00000101
(unsigned)~0 >> __builtin_clz(n)     = 00000111
(unsigned)~0 >> __builtin_clz(n) ^ n = 00000010

Discuss

https://leetcode.com/problems/number-complement/discuss/96017