Why Greedy Works and When It Fails in DSA Typescript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the next interval with the earliest finish time.

DSA Typescript

intervals.sort((a, b) => a.end [1] b.end);

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A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction in the sort comparator.

Sorting by start time instead of end time.

Sorting intervals by their end time requires subtracting b.end from a.end to get ascending order.

2fill in blank

medium

Complete the code to check if the current interval starts after the last selected interval ends.

DSA Typescript

if (interval.start [1] lastSelectedEnd) { selected.push(interval); lastSelectedEnd = interval.end; }

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A<=

B<

C>

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using >= instead of >, which allows overlapping intervals.

Using < or <=, which is incorrect for this condition.

We select the interval only if it starts after the last selected interval ends, so interval.start > lastSelectedEnd.

3fill in blank

hard

Fix the error in the greedy coin change algorithm that fails for non-standard coin sets.

DSA Typescript

function greedyChange(amount: number, coins: number[]): number[] {
  coins.sort((a, b) => b - a);
  const result: number[] = [];
  for (const coin of coins) {
    while (amount [1] coin) {
      amount -= coin;
      result.push(coin);
    }
  }
  return result;
}

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A>=

B<=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of >= causes missing exact matches.

Using < or <= causes infinite loops or no coins used.

The loop should run while amount is greater than or equal to the coin value to use that coin.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that filters words longer than 3 characters and maps to their lengths.

DSA Typescript

const lengths = { [1]: [2] for (const word of words) if (word.length > 3) };

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Aword

Bword.length

Cword.toUpperCase()

Dword.length > 3

Attempts:

3 left

💡 Hint

Common Mistakes

Using the condition as a key or value.

Using uppercase words as keys instead of original words.

The key is the word itself, and the value is its length.

5fill in blank

hard

Fill all three blanks to create a map filtering entries with positive values and mapping keys to uppercase.

DSA Typescript

const filteredMap = new Map(Object.entries(data)
  .filter(([[1], [2]]) => [2] > 0)
  .map(([[1], [2]]) => [[3], [2]])
);

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Akey

Bvalue

Ckey.toUpperCase()

Dvalue.toUpperCase()

Attempts:

3 left

💡 Hint

Common Mistakes

Using value.toUpperCase() which is invalid if value is a number.

Mixing up key and value in filter or map.

We destructure entries into key and value, filter by value > 0, and map keys to uppercase with their values.