To address common interval problems (since the original image is missing), here are solutions for two classic interval tasks:
1. Maximum Number of Non-Overlapping Intervals
Problem: Given a list of intervals, find the maximum number of non-overlapping intervals you can select.
Approach:
- Sort intervals by their end time (greedy choice: selecting intervals that end earlier leaves more room for others).
- Iterate through the sorted list, selecting intervals that start after (or at) the end of the last selected interval.
Code:
def max_non_overlapping(intervals):
if not intervals:
return 0
# Sort intervals by end time
intervals.sort(key=lambda x: x[1])
count = 1
last_end = intervals[0][1]
for s, e in intervals[1:]:
if s >= last_end: # Non-overlapping (adjacent allowed)
count +=1
last_end = e
return count
Example:
Input: [[1,3], [2,4], [3,5], [6,7]] → Output: 2 (select [1,3] and [6,7]).
2. Minimum Number of Points to Cover All Intervals
Problem: Find the smallest number of points such that every interval contains at least one point.
Approach:
- Sort intervals by their end time.
- Place a point at the end of the first interval (covers as many subsequent intervals as possible).
- Skip all intervals covered by this point, then repeat for the next uncovered interval.
Code:
def min_covering_points(intervals):
if not intervals:
return 0
intervals.sort(key=lambda x: x[1])
points = [intervals[0][1]]
last_point = intervals[0][1]
for s, e in intervals[1:]:
if s > last_point: # Not covered by the last point
points.append(e)
last_point = e
return len(points)
Example:
Input: [[1,3], [2,4], [3,5]] → Output: 1 (point at 3 covers all intervals).
These solutions are efficient (O(n log n) time due to sorting) and handle most interval-related scenarios. Adjust the conditions (e.g., s > last_end vs s >= last_end) based on whether adjacent intervals are considered overlapping.
Let me know if you need clarification on a specific problem!


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