LeetCode-Complement of Base 10 Integer

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Description：
Every non-negative integer N has a binary representation. For example, 5 can be represented as “101” in binary, 11 as “1011” in binary, and so on. Note that except for N = 0, there are no leading zeroes in any binary representation.

The complement of a binary representation is the number in binary you get when changing every 1 to a 0 and 0 to a 1. For example, the complement of “101” in binary is “010” in binary.

For a given number N in base-10, return the complement of it’s binary representation as a base-10 integer.

Example 1:

Input: 5
Output: 2
Explanation: 5 is "101" in binary, with complement "010" in binary, which is 2 in base-10.

Example 2:

Input: 7
Output: 0
Explanation: 7 is "111" in binary, with complement "000" in binary, which is 0 in base-10.

Example 3:

Input: 10
Output: 5
Explanation: 10 is "1010" in binary, with complement "0101" in binary, which is 5 in base-10.

Note:

• 0 <= N < 10^9

题意：将一个非负数的二进制表示中，有效位的1换为0，0换为1，返回生成的新的数；

解法：考虑利用移位操作，对非负数N判断最低位，返回相反的那个数后再乘以当前位置处对应的阶；对所有位进行相同的操作并累加知道N为0；这里需要注意到当N为0的时候的边界点；

Java

class Solution {
    public int bitwiseComplement(int N) {
        if (N == 0) {
            return 1;
        }
        int res = 0;
        int base = 1;
        while (N > 0) {
            int bit = (N & 0x01) == 1 ? 0 : 1;
            N >>= 1;
            res += base * bit;
            base *= 2;
        }
        
        return res;
    }
}