Why is this solution failing in first subtask even though I used long where it is needed. After that I used long for all the variables where they won’t even overflow as they were given in constraint as 1<=Ai,

Y<=10e9. The same solution with every data type set as long is passing here. Please explain.

You may refer this discussion for lunchtime problems

https://discuss.codechef.com/questions/118551/discuss-your-approach-november-lunchtime

@taran_1407 If you can please see where my answer is giving WA for first soluiton. It is just a naive implementation of the problem. I don’t know why it is giving WA for first solution and AC for second where I used long even where it is not needed.

The difference in both the solutions is the use of data types int vs long.

when you calculate (curr-l)*(r-curr) with curr, l and r upto 10e9, It overflows.

But when you use long, it doesn’t

The problem is in the following line:

- long sum = ((curr - l) * (r - curr));

You need to understand how the expression is evaluated. Assigning answer to the long variable does not make the calculation in long. Here curr is int, l is int and r is int. i.e. all variables are of int type. So, the expression is get evaluated in int only and then it is assigned to long variable-sum. To get evaluation in long, you need to either declare some variable in long type or use typecasting in expression. So, the correct expression is:

- long sum = ((long)(curr - l) * (r - curr));

Here, (curr-l) is typecasted to long, so (r-curr) is promoted to long from int and expression is get evaluated in long and then the answer is ansigned to long sum.

Thank you. Will keep this in mind from next time.