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Pseudo Code — Practice Tasks

All tasks: write pseudo code FIRST, then implement in Go, Java, and Python.

Beginner Tasks

Task 1: Write pseudo code to count how many even numbers are in an array, then implement.

FUNCTION countEvens(array)
    // Write your pseudo code here
END FUNCTION
  • Input: [1, 2, 3, 4, 5, 6]
  • Expected Output: 3
  • Evaluation: Correct pseudo code structure, clean loop, correct modulo

Task 2: Write pseudo code to check if a string is a palindrome, then implement.

  • Input: "racecar" → true, "hello" → false
  • Evaluation: Two-pointer approach in pseudo code, edge cases (empty, single char)

Task 3: Write pseudo code to find the second largest element in an array, then implement.

  • Input: [3, 7, 1, 9, 5] → 7
  • Evaluation: Single pass O(n), handle duplicates ([5, 5, 5] → no second largest)

Task 4: Write pseudo code to compute the sum of digits of a number, then implement.

  • Input: 12345 → 15
  • Evaluation: Correct use of modulo and division in pseudo code

Task 5: Write pseudo code to remove duplicates from a sorted array in-place, then implement.

  • Input: [1, 1, 2, 3, 3, 4] → [1, 2, 3, 4]
  • Evaluation: Two-pointer technique, O(n) time, O(1) extra space

Intermediate Tasks

Task 6: Write CLRS-style pseudo code for selection sort, then implement in all 3 languages.

  • Include line numbers
  • Prove correctness with a loop invariant
  • Analyze: O(n^2) time, O(1) space

Task 7: Write pseudo code for the "valid parentheses" problem, then implement.

  • Input: "({[]})" → true, "({[})" → false
  • Use a stack in pseudo code
  • Evaluation: Correct stack operations, all bracket types

Task 8: Write pseudo code for rotating an array by k positions, then implement.

  • Input: [1,2,3,4,5], k=2 → [4,5,1,2,3]
  • Show TWO approaches: extra array O(n) space, and reverse trick O(1) space

Task 9: Write pseudo code for matrix transposition, then implement.

  • Input: [[1,2,3],[4,5,6]] → [[1,4],[2,5],[3,6]]
  • Evaluation: Correct index mapping result[j][i] = matrix[i][j]

Task 10: Write pseudo code for converting a decimal number to any base (2-16), then implement.

  • Input: 255, base 16 → "FF"
  • Evaluation: Correct modulo/division loop, digit-to-char mapping

Advanced Tasks

Task 11: Write pseudo code for Dijkstra's algorithm, then implement.

  • Must include: priority queue, relaxation, visited set
  • Analyze: O((V+E) log V) time

Task 12: Write pseudo code for the 0/1 knapsack (DP), then implement.

  • Show both: top-down (memoization) and bottom-up (tabulation)
  • Trace the DP table for a small example

Task 13: Write pseudo code for topological sort using DFS, then implement.

  • Must handle: cycle detection
  • Evaluation: Correct DFS with gray/black coloring

Task 14: Translate the following CLRS pseudo code to all 3 languages:

QUICKSORT(A, p, r)
1  if p < r
2      q = PARTITION(A, p, r)
3      QUICKSORT(A, p, q - 1)
4      QUICKSORT(A, q + 1, r)

PARTITION(A, p, r)
1  x = A[r]                // pivot
2  i = p - 1
3  for j = p to r - 1
4      if A[j] <= x
5          i = i + 1
6          exchange A[i] with A[j]
7  exchange A[i + 1] with A[r]
8  return i + 1
  • Note: CLRS uses 1-based indexing. Adjust for 0-based in real code.

Task 15: Write pseudo code for a Trie (insert, search, startsWith), then implement.

  • Evaluation: Correct node structure, character-by-character traversal