Here is problem solution - https://programs.programmingoneonone.com/2021/07/hackerrank-hackerX-problem-solution.html

https://zeroplusfour.com/hackerx-hackerrank-solution/

Here's how I did in all languages Java 8 , C++ , C , Python 3, Python 2.

Python 3 code

n = int(input())
inp = (map(int, input().split()) for i in range(n))
p = sorted(list((a + b, a - b) for a, b in inp))
a = list(y for x, y in p)
d = []
for x in a:
    low, high = -1, len(d) # >, <=
    while high - low > 1:
        mid = (low + high) >> 1
        if d[mid] > x:
            low = mid
        else:
            high = mid
    if high == len(d):
        d.append(x)
    else:
        d[high] = x
print(len(d))

does an increase in the frequency by 1 for example means it's gonna take time of the same amount(1) to be adjusted? i mean if does an increase in frequency by 1 requires 1 unit of time ??

I have an algorithm what gives less than expected output, for example for case 4, it gives 15. And could not find a cause. All missiles are hit and enough spare time to change frequency. Have I missed something obvious?