Merge Overlapping Intervals in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort intervals by their start value.

DSA Rust

intervals.sort_by_key(|interval| interval.[1]);

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Astart

Bend

Clength

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Sorting by end instead of start causes incorrect merging order.

Using a non-existent field like 'length' or 'value'.

We sort intervals by their start value to process them in order.

2fill in blank

medium

Complete the code to check if two intervals overlap.

DSA Rust

if intervals[i].start <= merged.last().unwrap().[1] {

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Alength

Bstart

Cend

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with 'start' instead of 'end' of last merged interval.

Using incorrect field names.

Two intervals overlap if the current start is less than or equal to the last merged end.

3fill in blank

hard

Fix the error in updating the end of the last merged interval.

DSA Rust

merged.last_mut().unwrap().end = merged.last().unwrap().end.[1](intervals[i].end);

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Amax

Bmin

Csum

Dabs

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'min' causes incorrect merging by shortening intervals.

Using 'sum' or 'abs' is not meaningful here.

We update the end to the maximum to cover the full merged interval.

4fill in blank

hard

Fill both blanks to complete the loop that merges intervals.

DSA Rust

for i in [1]..intervals.len() {
    if intervals[i].start <= merged.last().unwrap().[2] {

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A1

B0

Cend

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Starting loop from 0 causes comparing interval with itself.

Comparing with 'start' instead of 'end' causes wrong overlap detection.

Loop starts from 1 to compare with previous intervals; compare current start with last merged end.

5fill in blank

hard

Fill all three blanks to complete the merging function.

DSA Rust

fn merge_intervals(mut intervals: Vec<Interval>) -> Vec<Interval> {
    intervals.sort_by_key(|interval| interval.[1]);
    let mut merged = vec![intervals[[2]].clone()];
    for i in [3]..intervals.len() {
        if intervals[i].start <= merged.last().unwrap().end {
            let last = merged.last_mut().unwrap();
            last.end = last.end.max(intervals[i].end);
        } else {
            merged.push(intervals[i].clone());
        }
    }
    merged
}

Drag options to blanks, or click blank then click option'

Astart

B0

C1

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'end' instead of 'start' for sorting.

Starting merged with wrong index.

Looping from 0 instead of 1.

Sort by start, initialize merged with first interval (index 0), loop from second interval (index 1).

Practice

1. What is the main goal when merging overlapping intervals in a list like [[1,3],[2,6],[8,10]]?

easy

A. Remove all intervals that overlap

B. Sort intervals by their end values only

C. Combine intervals that overlap into one continuous interval

D. Split intervals into smaller parts

Solution

1. Step 1: Understand overlapping intervals

   Intervals overlap if one starts before the other ends. For example, [1,3] and [2,6] overlap.

2. Step 2: Merge overlapping intervals

   We combine overlapping intervals into one that covers both, like merging [1,3] and [2,6] into [1,6].

3. Final Answer:

   Combine intervals that overlap into one continuous interval -> Option C

4. Quick Check:

   Merging overlapping intervals means combining them [OK]

Hint: Merge intervals by combining overlapping ranges [OK]

Common Mistakes:

• Sorting only by end values misses correct merges
• Removing intervals instead of merging
• Splitting intervals unnecessarily

2. Which Rust code snippet correctly sorts a vector of intervals by their start value before merging?

easy

A. intervals.sort_by_key(|interval| interval[0]);

B. intervals.sort();

C. intervals.sort_by(|a, b| b[0].cmp(&a[0]));

D. intervals.sort_by_key(|interval| interval[1]);

Solution

1. Step 1: Identify sorting by start value

   We want to sort intervals by their first element (start), so we use sort_by_key with interval[0].

2. Step 2: Check sorting direction and key

   intervals.sort_by_key(|interval| interval[0]); sorts ascending by start, which is correct. intervals.sort_by(|a, b| b[0].cmp(&a[0])); sorts descending, which is wrong. intervals.sort_by_key(|interval| interval[1]); sorts by end, not start.

3. Final Answer:

   intervals.sort_by_key(|interval| interval[0]); -> Option A

4. Quick Check:

   Sort by start value using sort_by_key(interval[0]) [OK]

Hint: Use sort_by_key with interval[0] to sort by start [OK]

Common Mistakes:

• Sorting by end instead of start
• Sorting descending instead of ascending
• Using sort() without key for nested vectors

3. What is the output of this Rust code that merges overlapping intervals?

let mut intervals = vec![vec![1,4], vec![2,5], vec![7,9]];
intervals.sort_by_key(|x| x[0]);
let mut merged = vec![];
for interval in intervals {
    if merged.is_empty() || merged.last().unwrap()[1] < interval[0] {
        merged.push(interval);
    } else {
        let last = merged.last_mut().unwrap();
        last[1] = last[1].max(interval[1]);
    }
}
println!("{:?}", merged);

medium

A. [[2,5], [7,9]]

B. [[1,4], [2,5], [7,9]]

C. [[1,9]]

D. [[1,5], [7,9]]

Solution

1. Step 1: Sort intervals by start

   Sorted intervals: [[1,4], [2,5], [7,9]] (already sorted).

2. Step 2: Merge overlapping intervals

   [1,4] and [2,5] overlap, merged to [1,5]. [7,9] does not overlap, so added as is.

3. Final Answer:

   [[1,5], [7,9]] -> Option D

4. Quick Check:

   Merged intervals = [[1,5], [7,9]] [OK]

Hint: Merge intervals by extending end if overlapping [OK]

Common Mistakes:

• Not merging overlapping intervals
• Merging non-overlapping intervals
• Incorrectly updating interval ends

4. Identify the bug in this Rust code for merging intervals:

let mut intervals = vec![vec![1,3], vec![2,4], vec![5,7]];
intervals.sort_by_key(|x| x[1]);
let mut merged = vec![];
for interval in intervals {
    if merged.is_empty() || merged.last().unwrap()[1] < interval[0] {
        merged.push(interval);
    } else {
        let last = merged.last_mut().unwrap();
        last[1] = last[1].max(interval[1]);
    }
}
println!("{:?}", merged);

medium

A. Sorting by end value causes incorrect merging

B. Using last_mut() causes a runtime error

C. The vector intervals is not mutable

D. The condition to check overlap is reversed

Solution

1. Step 1: Check sorting key

   The code sorts intervals by their end value, but merging requires sorting by start value to process intervals in order.

2. Step 2: Effect of wrong sorting

   Sorting by end causes intervals to be processed out of order, leading to missed merges or incorrect merges.

3. Final Answer:

   Sorting by end value causes incorrect merging -> Option A

4. Quick Check:

   Sort by start, not end, for correct merging [OK]

Hint: Always sort intervals by start before merging [OK]

Common Mistakes:

• Sorting by end instead of start
• Misusing mutable references
• Incorrect overlap condition

5. Given a list of intervals [[1,3],[2,4],[5,7],[6,8],[9,10]], write a Rust function to merge all overlapping intervals and return the merged list. What is the correct merged output?

hard

A. [[1,3],[2,4],[5,7],[6,8],[9,10]]

B. [[1,4],[5,8],[9,10]]

C. [[1,8],[9,10]]

D. [[1,4],[5,7],[6,8],[9,10]]

Solution

1. Step 1: Sort intervals by start

   Sorted intervals: [[1,3],[2,4],[5,7],[6,8],[9,10]] (already sorted).

2. Step 2: Merge overlapping intervals step-by-step

   Merge [1,3] and [2,4] to [1,4]. Merge [5,7] and [6,8] to [5,8]. [9,10] stays separate.

3. Final Answer:

   [[1,4],[5,8],[9,10]] -> Option B

4. Quick Check:

   Merge intervals by extending ends where overlapping [OK]

Hint: Merge intervals by sorting and extending ends [OK]

Common Mistakes:

• Not merging all overlapping intervals
• Merging non-overlapping intervals
• Incorrect final intervals after merge