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Formatted question description: https://leetcode.ca/all/476.html

476. Number Complement (Easy)

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

Note:

1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
2. You could assume no leading zero bit in the integer’s 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.

Companies:
Cloudera

Related Topics:
Bit Manipulation

Solution 1.

For example:

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

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

• Java
• C++
• Python
• Go

• class Solution {
      public int findComplement(int num) {
          int power = (int) (Math.log(num) / Math.log(2));
          long max = (long) Math.pow(2, power + 1) - 1;
          return (int) (max - num);
      }
  }
  
  ############
  
  class Solution {
      public int findComplement(int num) {
          int ans = 0;
          boolean find = false;
          for (int i = 30; i >= 0; --i) {
              int b = num & (1 << i);
              if (!find && b == 0) {
                  continue;
              }
              find = true;
              if (b == 0) {
                  ans |= (1 << i);
              }
          }
          return ans;
      }
  }
  

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

• class Solution(object):
    def findComplement(self, num):
      i = 1
      while i <= num:
        i = i << 1
      return (i - 1) ^ num
  
  

• func findComplement(num int) int {
  	ans := 0
  	find := false
  	for i := 30; i >= 0; i-- {
  		b := num & (1 << i)
  		if !find && b == 0 {
  			continue
  		}
  		find = true
  		if b == 0 {
  			ans |= (1 << i)
  		}
  	}
  	return ans
  }
  

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