Leetcode: Number Complement

Posted 2020-08-29 neverlandly

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

Note:
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.
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.

Better solution:

public static int highestOneBit(int i)

Returns an int value with at most a single one-bit, in the position of the highest-order ("leftmost") one-bit in the specified int value. 

1 public class Solution {
2     public int findComplement(int num) {
3         return ~num & ((Integer.highestOneBit(num) << 1) - 1);
4     }
5 }

一般方法：

 1 public class Solution {
 2     public int findComplement(int num) {
 3         int res = 0;
 4         int i = 31;
 5         while (i >= 0) {
 6             if (((num >>> i) & 1) == 1) break;
 7             i--;
 8         }
 9         while (i >= 0) {
10             if (((num >>> i) & 1) == 0) {
11                 res |= 1<<i;
12             }
13             i--;
14         }
15         return res;
16     }
17 }