Problems

A selection of problems implemented in TypeScript.

A — Array

1. 🟢 🙂 Contains Duplicate

• DS: Set
• Algorithm: Count difference in length.

2. 🟢 🙂 Valid Anagram

• DS: List
• Algorithm: Count frequency of each character.

3. 🟢 🙂 Two Sum

• DS: Map
• Algorithm: Test for compliment.

4. 🟠 🙂 Group Anagrams

• DS: Map
• Algorithm: Sort.

5. 🟠 🙂 Top K Frequent Elements

• DS: Map
• Algorithm: Sort.

6. 🟠 🙂 Product of Array Except Self

• DS: List
• Algorithm: Prefix & Postfix.

7. 🟠 🙂 Valid Soduko

• DS: Map of Sets
• Algorithm: Loop rows, columns to get cell. Test if cell is contained in respective row, column, or square set of values using a unique set key. Square keys are generated by banding and intersecting row and column indices using Math.floor and square dimension of 3: ${row}-${column}.

8. 🟠 😐 String Encode and Decode

• DS: List
• Algorithm: Nested while loop.

9. 🟠 🙂 Longest Consecutive Sequence

• DS: Set
• Algorithm:
  1. CREATE numbers Set.
  2. ITERATE numbers.
  3. GET sequence start. IF previous number IS NOT IN Set.
  4. SET sequence length IF longer THAN existing.
  5. RETURN sequence length.

B — Stack

1. 🟢 🙂 Valid Parentheses

• DS: Stack
• Algorithm:
  1. ITERATE brackets.
  2. IF open THEN push.
  3. ELSE IF pop != matching bracket THEN RETURN false.
  4. ELSE RETURN stack = empty.

2. 🟠 🙂 Min Stack

• DS: Stack x 2
• Algorithm:
  1. WHEN push IF value < MinStack top THEN push MinStack.
  2. WHEN pop IF value = MinStack top THEN pop MinStack.

3. 🟠 🙂 Evaluate Reverse Polish Notation

• DS: Stack
• Algorithm:
  1. IF operator THEN evaluate two integers on Stack.
  2. ELSE push integer to Stack.

4. 🟠 🙂 Generate Parentheses

• Heuristics: Backtracking, Recursion
• DS: Stack
• Algorithm: Call generator function recursively.

5. 🟠 🙁 Daily Temperatures

• Heuristics: Greedy
• DS: Stack
• Algorithm: ?

6. 🟠 🙂 Car Fleet

• Heuristics: Greedy
• DS: Stack
• Algorithm:
  1. Zip distance and speed.
  2. Sort descending distance.
  3. ITERATE zipped cars.
  4. Calculate ETA THEN push to Stack.
  5. IF car ETA < car ahead THEN pop and merge car from Stack.

C — Two Pointers

1. 🟢 🙂 Valid Palindrome

• Algorithm: Walk two pointers in opposite directions.

2. 🟢 🙂 Two Sum II - Input Array Is Sorted

• Algorithm:
  1. Walk two pointers in possite directions
  2. IF sum > target THEN decrease endPointer
  3. IF sum < target THEN increase startPointer