CODEWITHSUNDEEP
java
DoubleDown
DoubleDown

Reputation: 3

Not able to proceed with Series sum

I wanted to find the missing number in series so i thought a simple idea why not add all the numbers in array which are in series and hold it in one variable and then calculate the sum of series by formula Sn=n/2(a+l) but while calculating the series sum i am getting some error.

public class Missing {
    public static void main(String[] args) {


    int ar [] = {1,2,3,4,5,6,7,8,9,10,11,12,13};
    int sum = 0; int total=0;
    for(int num: ar)
    {
        sum = sum+num;
    }



        int n = ar.length;
        int a = ar[0];
        int l =ar[ar.length-1];
         total = [n/2*(a+l)];

         System.out.print("The missing number is "+(sum-total));

}}

total = [n/2*(a+l)]; ............................(1)

This is where i am getting error.

enter image description here

Upvotes: 0

Views: 86

Answers (3)

Prajwal
Prajwal

Reputation: 256

If you don't want to use my above logic. You have to make changes to your code: Edit this:

int n = ar.length+1;

n has been assigned ar.length + 1 because that +1 is needed to compensate for the missing element in the array list

Also, the formula has not been correctly written into the code:

total = (n* (a + l))/2;

If you first divide n by 2 then, it will truncate the places after decimal point because n is an integer not a floating number. So, your logic would fail when n is not even.

And lastly, the missing number would be (sum-total) not the other way around because 'total' contains the missing number and 'sum' does not.

System.out.print("The missing number is "+(total-sum));

Upvotes: 0

Prajwal
Prajwal

Reputation: 256

You can use the below logic which is much simpler to use and understand

for(int i=0;i<ar.length-1;i++)
{
        if(ar[i]!=ar[i+1]-1)
        {   
            System.out.print("The missing number is "+(ar[i]+1)+"\n");
            break;
        }
}

Upvotes: 1

StaticBeagle
StaticBeagle

Reputation: 5185

The first thing is in total = [n/2*(a+l)]; [] is not valid syntax in this context. The second thing I noticed, is that your formula to calculate the sum seems odd, maybe you meant Sn = (n * (a + l)) / 2?. After making those two changes the code should look as follows:

public class Missing {
    public static void main(String[] args) {

        int ar [] = {1,2,3,4,5,6,7,8,9,10,11,12,13};
        int sum = 0; 
        for(int num: ar)
        {
            sum = sum+num;
        }

        int n = ar.length;
        int a = ar[0];
        int l =ar[ar.length - 1];
        int total = (n * (a + l)) / 2;
        System.out.print("The missing number is "+(sum - total));
        // outputs 0 which is correct nothing is missing

        // Now if you remove say 12 from the array
        // by changing the array to int ar [] = {1,2,3,4,5,6,7,8,9,10,11,0,13};
        // you should get back -12 which means 12 is missing
    }
}

Upvotes: 0

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