【leetcode】476. Number Complement
The complement of an integer is the integer you get when you flip all the 0
's to 1
's and all the 1
's to 0
's in its binary representation.
- For example, The integer
5
is"101"
in binary and its complement is"010"
which is the integer2
.
Given an integer num
, return its complement.
Example 1:
Input: num = 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.
这题考察对于数字基本的位存储的信息,依次取出数字的最低位,如果是0则翻转相加,index记录当前的阶数,num补零右移,直到为0位置。
class Solution {
public:
int findComplement(int num) {
int index=0;
int tmp=0;
while(num){
if((num&1)==0){
tmp=tmp+pow(2,index);
}
num=num>>1;
index++;
}
return tmp;
}
};
还有一种更加trick的处理方式。利用bit mask的方式计算
class Solution {
public:
int findComplement(int num) {
unsigned mask = ~0;
while( mask & num ) mask = mask << 1;
return ~num ^ mask;
}
};