Complement of Base 10 Integer in C++

The complement of an integer is the integer you get when you flip all the 0’s to 1 ‘s and all the 1s 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.

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class Solution {
   int bitwiseComplement(int n) {
   int m = n;
   int mask = 0;

    //edge case
    if(n== 0)
     return 1;
    while( m!=0) {
       mask = (mask << 1) | 1;
       m = m >> 1;
    int ans = (~n) & mask;
    return ans;

Approach: Here the number is converted by flipping bits and adding that power of 2 to the answer. Follow the steps mentioned below to implement it:

  • Find the binary representation of N.
  • For each bit, flip it and add the contribution of this bit to the final answer.
  • Return the final answer

Time Complexity: O(logN)
Auxiliary Space: O(1)

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