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476. Number Complement
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.
idea: we only want to flip the lower k bits (k is the bits number of num)
Solution 1: use mask to find the leftmost 1 of num, and then use ~mask to make only the k lowest bits to be 1(k is the bits number of num), and then & ~num to get the result.
class Solution { public: int findComplement(int num) { unsigned mask=INT_MAX; while((mask&num)!=0){ mask= mask << 1; } return (~mask & ~num); } };
Solution 2: the needed mask is (2^(int)log(num))-1=(1<<(int)log(num))-1
class Solution { public: int findComplement(int num) { return ~num & ((1 <<(int)log2(num))-1); } };
476. Number Complement