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Formatted question description: https://leetcode.ca/all/1009.html
1009. Complement of Base 10 Integer
Level
Easy
Description
Every nonnegative 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 base10, return the complement of its binary representation as a base10 integer.
Example 1:
Input: 5
Output: 2
Explanation: 5 is “101” in binary, with complement “010” in binary, which is 2 in base10.
Example 2:
Input: 7
Output: 0
Explanation: 7 is “111” in binary, with complement “000” in binary, which is 0 in base10.
Example 3:
Input: 10
Output: 5
Explanation: 10 is “1010” in binary, with complement “0101” in binary, which is 5 in base10.
Note:
0 <= N < 10^9
Solution
Since the complement of 0
is 1
and the complement of 1
is 0
, simply deal with these two numbers first.
For the other nonnegative integers, consider the number of bits in binary representation, which can be calculated by using log_{2}N + 1 for integer N
(keep the integer part of the calculated result). For a number with b
bits in binary representation, the sum of the number and its complement equals 2^{b}  1, so the complement equals 2^{b}  1 minus the given number.

class Solution { public int bitwiseComplement(int N) { if (N <= 1) return 1  N; int power = (int) (Math.log(N) / Math.log(2)); int max = (int) (Math.pow(2, power + 1)  1); return max  N; } }

// OJ: https://leetcode.com/problems/complementofbase10integer/ // Time: O(1) // Space: O(1) class Solution { public: int bitwiseComplement(int n) { if (n == 0) return 1; unsigned mask = ~0; while (mask & n) mask <<= 1; return ~mask & ~n; } };

class Solution: def bitwiseComplement(self, n: int) > int: if n == 0: return 1 ans = 0 find = False for i in range(30, 1, 1): b = n & (1 << i) if not find and b == 0: continue find = True if b == 0: ans = 1 << i return ans ############ # 1009. Complement of Base 10 Integer # https://leetcode.com/problems/complementofbase10integer/ class Solution: def bitwiseComplement(self, n: int) > int: if n == 0: return 1 full = (1 << n.bit_length())  1 return full ^ n