Question

476. Number Complement

中文文档

Description

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 integer 2.

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.

Example 2:

Input: num = 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.

 

Constraints:

• 1 <= num < 231

 

Note: This question is the same as 1009: https://leetcode.com/problems/complement-of-base-10-integer/

Solutions

Solution 1

class Solution:
  def findComplement(self, num: int) -> int:
    ans = 0
    find = False
    for i in range(30, -1, -1):
      b = num & (1 << i)
      if not find and b == 0:
        continue
      find = True
      if b == 0:
        ans |= 1 << i
    return ans

class Solution {
  public int findComplement(int num) {
    int ans = 0;
    boolean find = false;
    for (int i = 30; i >= 0; --i) {
      int b = num & (1 << i);
      if (!find && b == 0) {
        continue;
      }
      find = true;
      if (b == 0) {
        ans |= (1 << i);
      }
    }
    return ans;
  }
}

class Solution {
public:
  int findComplement(int num) {
    int full = pow(2, int(log2(num)) + 1) - 1;
    return full ^ num;
  }
};

func findComplement(num int) int {
  ans := 0
  find := false
  for i := 30; i >= 0; i-- {
    b := num & (1 << i)
    if !find && b == 0 {
      continue
    }
    find = true
    if b == 0 {
      ans |= (1 << i)
    }
  }
  return ans
}

Solution 2

class Solution:
  def findComplement(self, num: int) -> int:
    return num ^ (2 ** (len(bin(num)[2:])) - 1)

class Solution {
public:
  int findComplement(int num) {
    int ans = 0;
    bool find = false;
    for (int i = 30; i >= 0; --i) {
      int b = num & (1 << i);
      if (!find && b == 0) continue;
      find = true;
      if (b == 0) ans |= (1 << i);
    }
    return ans;
  }
};