342. Power of Four

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Solution 1

The Key Idea for Solving This Coding Question

Satisfy following three conditions

1. num is postive integer
2. num is power of 2.
3. This power of 2 is even power.

C++ Code

class Solution {
public:
    bool isPowerOfFour(int num) {
        return num > 0 &&                                         // condition 1
               (num & (num - 1)) == 0 &&                          // condition 2
               (0b01010101010101010101010101010101 & num) == num; // condition 3
    }
};

Time Complexity

$O(1)$

Space Complexity

$O(1)$

Solution 2

The Key Idea for Solving This Coding Question

C++ Code

class Solution {
public:
    bool isPowerOfFour(int n) {
        if (n <= 0) {
            return false;
        }
        
        while (n > 1) {
            if (n % 4) {
                return false;
            }
            n = n / 4;
        }
        
        return true;
    }
};

Time Complexity

$O(1)$

Space Complexity

$O(1)$

Solution 3

The Key Idea for Solving This Coding Question

C++ Code

class Solution {
public:
    bool isPowerOfFour(int n) {
        if (n <= 0) {
            return false;
        }
        if (n == 1) {
            return true;
        }
        if (n % 4) {
            return false;
        }
        return isPowerOfFour(n / 4);
    }
};

Time Complexity

$O(1)$

Space Complexity

$O(1)$

Miscellaneous