You are given a 2D integer array ranges
where ranges[i] = [starti, endi]
denotes that all integers between starti
and endi
(both inclusive) are contained in the ith
range.
You are to split ranges
into two (possibly empty) groups such that:
Two ranges are said to be overlapping if there exists at least one integer that is present in both ranges.
[1, 3]
and [2, 5]
are overlapping because 2
and 3
occur in both ranges.Return the total number of ways to split ranges
into two groups. Since the answer may be very large, return it modulo 109 + 7
.
Example 1:
Input: ranges = [[6,10],[5,15]] Output: 2 Explanation: The two ranges are overlapping, so they must be in the same group. Thus, there are two possible ways: - Put both the ranges together in group 1. - Put both the ranges together in group 2.
Example 2:
Input: ranges = [[1,3],[10,20],[2,5],[4,8]] Output: 4 Explanation: Ranges [1,3], and [2,5] are overlapping. So, they must be in the same group. Again, ranges [2,5] and [4,8] are also overlapping. So, they must also be in the same group. Thus, there are four possible ways to group them: - All the ranges in group 1. - All the ranges in group 2. - Ranges [1,3], [2,5], and [4,8] in group 1 and [10,20] in group 2. - Ranges [1,3], [2,5], and [4,8] in group 2 and [10,20] in group 1.
Constraints:
1 <= ranges.length <= 105
ranges[i].length == 2
0 <= starti <= endi <= 109
When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:
The brute force method for grouping overlapping ranges involves trying every possible grouping. We consider each range individually, deciding whether to group it with a prior group or start a new one. This exhaustive exploration guarantees we find all valid groupings, even if it's incredibly inefficient.
Here's how the algorithm would work step-by-step:
def count_grouping_ways_brute_force(ranges):
number_of_ranges = len(ranges)
count = 0
def overlap(range1, range2):
return not (range1[1] < range2[0] or range2[1] < range1[0])
def solve(index, current_groups):
nonlocal count
# Base case: all ranges have been processed
if index == number_of_ranges:
count += 1
return
# Try adding the current range to existing groups
for group_index in range(len(current_groups)):
can_add_to_group = True
for existing_range in current_groups[group_index]:
if not overlap(ranges[index], existing_range):
continue
else:
break
else:
# Create a new copy of the groups and add the current range.
new_groups = [group[:] for group in current_groups]
new_groups[group_index].append(ranges[index])
solve(index + 1, new_groups)
# Always consider starting a new group
# This ensures that every possibility is explored
new_groups = [group[:] for group in current_groups]
new_groups.append([ranges[index]])
solve(index + 1, new_groups)
# Start with an empty list of groups.
solve(0, [])
return count
The key idea is to realize overlapping ranges can be merged into single, larger ranges. We can efficiently count the ways to group these merged ranges by understanding that each group represents a 'yes/no' decision: either it's in a group, or it isn't.
Here's how the algorithm would work step-by-step:
def count_grouping_ways(ranges):
ranges.sort(key=lambda interval: interval[0])
merged_ranges = []
for interval in ranges:
if not merged_ranges or interval[0] > merged_ranges[-1][1]:
merged_ranges.append(interval)
else:
merged_ranges[-1] = [merged_ranges[-1][0], max(merged_ranges[-1][1], interval[1])]
# The number of independent ranges determines the exponent for 2.
number_of_independent_ranges = len(merged_ranges)
#Calculate the total number of ways to group the ranges.
total_ways = pow(2, number_of_independent_ranges)
return total_ways
Case | How to Handle |
---|---|
ranges is null or empty | Return 1, representing an empty grouping which is one possible way. |
ranges contains only one range | Return 2, representing either including the range in a group or not including it (empty group). |
All ranges are non-overlapping | The number of ways to group is 2 raised to the power of the number of ranges; calculate this using modular exponentiation. |
All ranges are completely overlapping (e.g., [[0, 5], [1, 4], [2, 3]]) | The number of ways to group is 2 since all ranges must be in the same group or all not in any group. |
ranges contains very large numbers, potentially causing integer overflow | Use long data type where necessary to prevent overflow, especially during calculations such as modular exponentiation, and always take the modulo at each step. |
ranges is extremely large (many ranges) | Ensure the algorithm has a time complexity of O(n log n) or better by using efficient sorting and merging techniques. |
ranges contains negative numbers | The algorithm should handle negative numbers correctly, especially when sorting and comparing ranges. |
ranges contains overlapping ranges that are identical (e.g., [[1, 5], [1, 5]]) | Treat the duplicates as distinct ranges when calculating the number of possible groupings. |