Minimum One Bit Operations to Make Integers Zero

Updated on 17 June, 2025
Minimum One Bit Operations to Make Integers Zero header image

Problem Statement

Given an integer n, the goal is to reduce it to 0. The process includes using specific operations that modify the bits of n's binary representation. Two main operations are permissible:

  1. Change the rightmost (0th) bit.
  2. Change the ith bit only if certain conditions regarding the preceding bits are met: the (i−1)th bit must be 1, and all bits from (i-2)th to 0th must be 0.

The objective is to determine the minimum number of these operations required to completely transform the integer n into 0.

Examples

Example 1

Input:

n = 3

Output:

2

Explanation:

The binary representation of 3 is "11".
"11" -> "01" with the 2nd operation since the 0th bit is 1.
"01" -> "00" with the 1st operation.

Example 2

Input:

n = 6

Output:

4

Explanation:

The binary representation of 6 is "110".
"110" -> "010" with the 2nd operation since the 1st bit is 1 and 0th through 0th bits are 0.
"010" -> "011" with the 1st operation.
"011" -> "001" with the 2nd operation since the 0th bit is 1.
"001" -> "000" with the 1st operation.

Constraints

  • 0 <= n <= 109

Approach and Intuition

The approach to solving this problem is largely based on optimizing the use of the allowed bit operations to minimize the number of steps needed. From the examples provided, it is clear that understanding the binary representation of n is crucial as the operations are bit-sensitive. Here is a more detailed breakdown of the problem-solving intuition:

  1. Start by observing the least significant bit (LSB or the 0th bit). If this bit is 1, it can be toggled immediately. This is the simplest and always available operation, making it a consistent first step when the LSB is 1.

  2. For any other bit (let’s consider ith bit where i > 0), the conditions for its manipulation are more complex:

    • The directly preceding bit (i-1) must be 1.
    • All bits from (i-2) to the 0th position must be 0.

    These constraints mean that changes to higher order bits can only happen under more restricted circumstances.

  3. From the given examples:

    • For n = 3 (binary "11"): The reduction sequence highlights a cascading effect where higher bit changes influence lesser bits. You start by manipulating the highest allowed bit (under the defined operations) and then address the resulting changes, moving progressively downwards towards the LSB.
    • For n = 6 (binary "110"): The necessary steps show a pattern of toggling termed "back and forth" on the least significant bits induced by the conditionally permitted operations on higher bits.
  4. The best approach seems to involve:

    • Continually addressing the LSB whenever possible.
    • Using the allowed operations to change higher bits strategically, triggering conditions that allow subsequent operations on bits lower down the hierarchy.

Realizing this pattern and strategically applying operations can minimize the number of steps, providing an efficient solution in potentially logarithmic time concerning the number of bits in n.

Solutions

  • C++
  • Java
  • Python
cpp
class Solution {
public:
    int minBitOperations(int number) {
        int result = number;
        result ^= result >> 16;
        result ^= result >> 8;
        result ^= result >> 4;
        result ^= result >> 2;
        result ^= result >> 1;
        return result;
    }
};

This C++ solution details an approach to determine the minimum number of bit operations required to convert a given integer to zero. The strategy employed involves repeatedly using bit-wise XOR operations on progressively right-shifted versions of the integer. Here’s how you understand the process:

  • Start with the input number.
  • Perform a XOR operation between number and number right-shifted by 16. Store the result back in number.
  • Repeat the XOR operation with the result right-shifted by progressively smaller exponents: 8, 4, 2, and finally 1.

Each XOR operation essentially reduces the number of one-bits through combining pairs of bits, hence moving closer to zero with each step. The final result from the sequence of operations gives the minimal number of operations needed. The function returns this result. The code itself is compact and executes efficiently by reducing the problem size logarithmically, adjusting the scope of XOR operations through the use of right shifts.

java
class Solution {
    public int minOneBitConversion(int n) {
        int result = n;
        result ^= result >> 16;
        result ^= result >> 8;
        result ^= result >> 4;
        result ^= result >> 2;
        result ^= result >> 1;
        return result;
    }
}

The solution provided in Java addresses the problem of determining the minimum one-bit operations required to transform an integer into zero using bitwise operations. The function minOneBitConversion(int n) calculates this by repeatedly applying bitwise XOR operations. Each XOR operation is performed between the current result and the result right-shifted by increasing powers of two (1, 2, 4, 8, 16). This technique cleverly utilizes the properties of XOR to gradually reduce the number by isolating and eliminating bits from evaluation, leading to the final result which is a derivative of the input number transformed in such a way to minimize operations. Finally, the method returns the result after processing all shifts, providing the minimum number of operations needed.

python
class Solution:
    def minBitFlips(self, number: int) -> int:
        result = number
        result ^= result >> 16
        result ^= result >> 8
        result ^= result >> 4
        result ^= result >> 2
        result ^= result >> 1
        return result

The Python code presented solves the problem of determining the minimum one-bit operations required to convert an integer to zero. The function minBitFlips takes an integer number as an argument and utilizes bit manipulation to calculate the minimum operations.

  • The process starts by assigning the input number to a variable result.
  • It then enters a series of XOR operations, each time shifting result right by an increasingly smaller power of two (from 16 down to 1).
  • These operations sequentially reduce result by flipping differing sets of bits.

Each of the bit shift operations aims to isolate and manipulate individual bits of the integer, exploiting the properties of XOR to effectively count the bits that need to be flipped. The final return gives the count of these operations, representing the answer to the problem. This function is efficient, harnessing bitwise operations for a quick computation that runs in constant time relative to the size of the integer.

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