CODEWITHSUNDEEP
javapow
Pazhani_Kumar
Pazhani_Kumar

Reputation: 11

Power of 2 Program in java giving true if i pass number as 2147483647 why?

I have tried writing a java program to find a number is power of two the one which i mentioned below.

I am passing number as 2147483647 and the output of my program is returning true instead of false. Can anyone explain what concept I am missing here and how to correct it.

Program

class Solution {
    public boolean isPowerOfTwo(int n) {
        int num = 0;
        int p = 0;
        while(num <= n){
            num = (int) Math.pow(2,p);
            p++;
            if(num == n){
            return true;
        }
        }
        
        return false;    

    }
}

    public static void main(String[] args) {
    
        enter code here
        boolean val = isPowerOfTwo(2147483647);
    
        }

Upvotes: 1

Views: 96

Answers (1)

Louis Wasserman
Louis Wasserman

Reputation: 198004

If a double is greater than Integer.MAX_VALUE, then casting it to an int will give you Integer.MAX_VALUE.

The number you give is Integer.MAX_VALUE, so of course it's going to be equal to sufficiently large values of (int) Math.pow(2, p).

You will need a different approach, such as actually doubling an int value instead of just calling Math.pow, or some more sophisticated approach. (The usual ultra-optimized solution is x >= 0 && (x & (x - 1)) == 0, but you probably won't understand that or why it works yet.)

Upvotes: 4

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