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Power of Two

Problem Description​

Given an integer n, return true if it is a power of two. Otherwise, return false.

An integer n is a power of two if there exists an integer x such that n == 2^x.

Example​

Example 1:

Input: n = 1
Output: true
Explanation: 2^0 = 1

Example 2:

Input: n = 16
Output: true
Explanation: 2^4 = 16

Example 3:

Input: n = 3
Output: false

Example 4:

Input: n = 4
Output: true

Example 5:

Input: n = 5
Output: false

Constraints​

  • -2^31 <= n <= 2^31 - 1

Solution Approach​

Approach Overview​

To determine if a number n is a power of two, we can use bit manipulation. A number is a power of two if it has exactly one 1 bit in its binary representation. For example:

  • 2 in binary is 10
  • 4 in binary is 100
  • 8 in binary is 1000

If n is a power of two, n & (n - 1) should be 0. This is because subtracting 1 from a power of two flips all bits after the rightmost 1 (including the rightmost 1 itself).

Detailed Steps​

  1. Check if n is greater than 0.
  2. Use the bitwise AND operation n & (n - 1).
  3. If the result is 0, then n is a power of two.

Code Examples​

C++​

class Solution {
public:
    bool isPowerOfTwo(int n) {
        // A number n is a power of two if:
        // 1. n is greater than 0
        // 2. n & (n - 1) is equal to 0
        return n > 0 && (n & (n - 1)) == 0;
    }
};

Python​

class Solution:
    def isPowerOfTwo(self, n: int) -> bool:
        # A number n is a power of two if:
        # 1. n is greater than 0
        # 2. n & (n - 1) is equal to 0
        return n > 0 and (n & (n - 1)) == 0

Java​

class Solution {
    public boolean isPowerOfTwo(int n) {
        // A number n is a power of two if:
        // 1. n is greater than 0
        // 2. n & (n - 1) is equal to 0
        return n > 0 && (n & (n - 1)) == 0;
    }
}

C​

#include <stdbool.h>

bool isPowerOfTwo(int n) {
    // A number n is a power of two if:
    // 1. n is greater than 0
    // 2. n & (n - 1) is equal to 0
    return n > 0 && (n & (n - 1)) == 0;
}

Complexity​

  • Time Complexity: O(1), because the number of operations is constant and does not depend on the size of the input.
  • Space Complexity: O(1), because no additional space is used beyond a few integer variables.