Now I get it, I was misinterpreting question all this time. Actually after finish of each round, lead is not the difference between points of that round. But the lead is difference between the points achieved through all rounds including current round - Lakpa Tashi Bhutia
This is more optimum than the easy solution. In this solution, I don't have to calculate the cumulative sum for both players. I am just calculating the cumulative difference that is lead. If diff is positive p1 wins else p2 wins. Max lead will be the max |diff|.
Here is my solution to this problem which actually teaches you how useful stack can be for such problems (although this problem can be solved without using stack, my code rather tries to teach people starting out the usage of stack and bracket matching).