I am trying to find help assigning an element of a list to another. To be specific, I am doing the "Sum of Intervals" challenge on Codewars.

Write a function called sumIntervals/sum_intervals() that accepts an array of intervals, and returns the sum of all the interval lengths. Overlapping intervals should only be counted once.

Intervals

Intervals are represented by a pair of integers in the form of an array. The first value of the interval will always be less than the second value. Interval example: [1, 5] is an interval from 1 to 5. The length of this interval is 4.

Overlapping Intervals

List containing overlapping intervals:

[
  [1,4],
  [7, 10],
  [3, 5]
]

The sum of the lengths of these intervals is 7. Since [1, 4] and [3, 5] overlap, we can treat the interval as [1, 5], which has a length of 4.

I am confused as to why trying to assign an element of a list to another fails. Here is my code:

def sum_of_intervals(intervals):
    sum = 0
    for thing in intervals:
        thing = list(thing)
        for thing2 in intervals:
            thing2 = list(thing2)
            if thing[1] > thing2[0] and thing[1] < thing2[1]:
                if thing == thing2 and intervals.index(thing) != intervals.index(thing2):
                    intervals.remove(tuple(thing2))
                else:
                    thing[1] = thing2[1] #line that does not seem to be working
                    intervals.remove(tuple(thing2))
    for thing3 in intervals:
        sum  = thing[1] - thing[0]
    return sum

Does anyone know why thing[1] = thing2[2] does not work? If I return intervals instead of sum, for example for ([(1,5),(3,7)]) it just returns (1, 5) or sum of 4.

If this question has been asked before (which it does not look like it has) please tell me and guide me there. Thank you!

CodePudding user response：

The fact that the intervals contain only integers is a gross simplification of the task. It can be solved in one line:

sum_of_intervals = lambda x: len(set.union(*[set(list(range(*i))) for i in x]))

CodePudding user response：

As previous comments/posts pointed out there are multiple issues with the original code (syntax and logic), and it's really hard (if not impossible) to follow it.

NB - never try to use the Python built-in sum as the variable name, also choose some meaningful variable names to convey the logic too.

So instead of try to enumerate them (the problems) one by one, I just want to point out there is simple way to solve the puzzle. That is to sorted the intervals (list of lists), and compare the starting and ending point then increment the size (length) along the loop. You can compare and try to see the difference.

The solution will be like this:

def sum_of_intervals(intervals):
    size, end = 0, float("-inf")
    
    for s, e in sorted(intervals):
        if s > end: 
            end  = s
        if e > end: 
            size  = e  - end
            end = e
    return size

Output:

print(sum_of_intervals(LoL))    #  7      LoL is your sample input.