/* https://leetcode.com/problems/number-complement/ Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation. The given integer is guaranteed to fit within the range of a 32-bit signed integer. You could assume no leading zero bit in the integer’s binary representation. highestOneBit(num) is the number with only the highest bit of num set. Subtract 1 to set all lower bits. This creates a mask. AND of mask with ~num sets all bits that were not set in num. Time - O(log n) Space - O(1) */ public class Solution { public int findComplement(int num) { return ~num & (Integer.highestOneBit(num) - 1); } }