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Greedy Algorithm Visualizer

Interactive tool to master the Interval Scheduling pattern. Visualize how sorting by end time and selecting non-overlapping intervals works step-by-step.

Interval Scheduling Visualizer

Find maximum non-overlapping intervals (Greedy: Sort by End Time)

Step 1 / 17
Start: Unsorted intervals
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[1, 3]
[2, 4]
[3, 5]
[0, 6]
[5, 7]
[8, 9]
[5, 9]

status

Unsorted

last end

-1
Python
def interval_scheduling(intervals):
    # Sort by end time
    intervals.sort(key=lambda x: x[1])
    
    count = 0
    last_end = -1
    
    for start, end in intervals:
        # If no overlap with last selected
        if start >= last_end:
            count += 1
            last_end = end
            # Select this interval
        else:
            # Skip this interval
            pass
            
    return count

Understanding Interval Scheduling

Interval Scheduling is the quintessential problem for understanding greedy algorithms. The goal is to select the maximum number of non-overlapping intervals. The seemingly simple strategy of “always pick the interval that ends earliest” is guaranteed to produce an optimal solution.

Why Sort by End Time?

Maximizing Future Capacity

By picking the interval that finishes earliest, you leave the maximum possible room for subsequent intervals. This resource maximization is the heart of the greedy choice property.

Other Sorts Fail

Sorting by start time or duration doesn't work. A short interval might overlap with everything, and an early starting interval might run forever. Only end-time sorting works for this problem.

Greedy Choice Property

A problem has the Greedy Choice Property if a global optimal solution can be arrived at by selecting a local optimal (greedy) choice. In Interval Scheduling, selecting the earliest finishing interval is always a safe move that is part of some optimal solution.

How to Use the Visualizer

  • Use Next/Previous buttons to step through the algorithm
  • Observe the Sort by End Time step first
  • Watch the decision making: compare start_time with last_end_time
  • Green intervals are selected; Red/crossed-out intervals are skipped due to overlap
  • Use Auto Play to see the smooth progression of the algorithm

Practice Problems

Apply what you've learned with these LeetCode problems:

•
Non-overlapping Intervals (LC 435) - Same pattern (count removals)
•
Minimum Arrows to Burst Balloons (LC 452) - Touching intervals variant
•
Meeting Rooms II (LC 253) - Resource allocation pattern

Learn More

Explore our comprehensive greedy algorithm tutorials and guides:

Complete Greedy Algorithm GuideWhy Sort By End Time (Proof)All Greedy Algorithm Tutorials

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