Finding Number Complements using Java

The problem

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

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:

  • The given integer num is guaranteed to fit within the range of a 32-bit signed integer.
  • num >= 1
  • You could assume no leading zero bit in the integer’s binary representation.

The code

// Our method that takes in an `int` and returns an `int`
public int findComplement(int num) {
    // Duplicate the input for reference
    int originalNum = num;

    // Set a variable for looping on an index
    long i = 1;
    // Loop while `i` is less or equal to `originalNum`
    while(i<=originalNum) {
        // Shift the variables
        num ^= i;
        i <<= 1;
    }
    // Return the resultant `num`
    return num;
}
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