【leetcode】【套路題】476. Number Complement
阿新 • • 發佈:2018-11-01
一、題目描述
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.
思路:這種題沒什麼辦法,記住這個套路吧。舉個例子,num = 00000101時,另mask = ~0 = 11111111,讓mask變為 11111000,然後計算~mask & ~num即可得到結果
程式碼:
class Solution { public: int findComplement(int num) { unsigned mask = ~0; while(mask & num){ mask = mask << 1; } return ~mask & ~num; } };