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Find the First Unique Element in a Stream of Characters at any Given Point

Aniruddha Chaudhari/567/0
CodePython

Problem Statement: Find the first unique element in a stream of characters at any given point.

Input:  a b c d a b c
Output: a a a a b c d

This competitive coding challenge was asked in the Flipkart SDE coding interview round.

Solution

The most efficient solution to this problem is to solve it with the doubly linked list.

You can use any programming language like C/C++, Python, Java, etc to solve this coding question.

Here is the Python code to solve this problem. I have added precise comments describing each line.

Python code:

# Find the first unique element in a stream of characters 
# at any given point.

MAX_CHAR_SIZE = 256

def find_first_unique_char(msg):

    # charDLL is doubly linked list.
    # if x is present in DLL, charDLL[x] contains pointer to a DLL node. 
    # If x is not present in DLL, then charDLL[x] is NULL
    charDLL = [] * MAX_CHAR_SIZE

	# repeated is the list of boolean values.
    # Here, repeated[x] is true if x is repeated two or more times. 
    # Else, False
    
    repeated = [False] * MAX_CHAR_SIZE

    out = ""
    for i in range(len(msg)):
        ch = msg[i]

        # We process this character only if it has nomat occurred
        # or occurred only once. repeated[x] is true if x is
        # repeated twice or more.
        if not repeated[ord(ch)]:

            # If the character is not in charDLL, then add this
            # at the end of DLL
            if not ch in charDLL:
                charDLL.append(ch)
            else:
                charDLL.remove(ch)
                repeated[ord(ch)] = True

        if len(charDLL) != 0:
            out += charDLL[0]

    return out



msgs = ["abcdabc", "csestacklearnprogrammingpracticaly"]
for msg in msgs:
    print("\nInput string:")
    print(msg)
    print("Output string:")
    out = find_first_unique_char(msg)
    print(out)

Output:

Input string:
abcdabc
Output string:
aaaabcd

Input string:
csestacklearnprogrammingpracticaly
Output string:
cccccceeetttttttttttttttttttkkkkkk

Try giving different input by covering all the corner cases.

The code is self-explanatory with the comments I have added. If you still have any doubts, let’s discuss them in the comment section below.

Python Interview Questions eBook

coding challenge
Aniruddha Chaudhari
I am complete Python Nut, love Linux and vim as an editor. I hold a Master of Computer Science from NIT Trichy. I dabble in C/C++, Java too. I keep sharing my coding knowledge and my own experience on CSEstack.org portal.

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Why?

Why Competitive Programming Important?

Coding Challenges for Practice

  1. Count Common Factor
  2. Does it Divide
  3. Sum of Sub Arrays
  4. Pair of Desired Sum
  5. Remove Duplicate Char from String
  6. Sort String by Char Freq (Python)
  7. Sort String by Char Freq (Java)
  8. Split Array into Equal Sum Subarray
  9. Validate IP Address
  10. Validate PAN Card Number
  11. Validate Sudoku
  12. Sort Circular Rotated Array
  13. String Permutations
  14. Min Arrow to Burst Bubbles
  15. Min Cost to Paint All Houses [Amazon]
  16. HourGlass with Max Sum
  17. Max Profit by Buying/Selling Stocks
  18. Hailstone Sequence
  19. Reverse String without affecting Special Characters
  20. Secure Conversation by Encry/Decry
  21. Special Elements in Matrix
  22. Next Greater No with Same set of Digits
  23. Smallest Subarray with Sum Greater than Given Number
  24. Group Anagrams
  25. Find Duplicates in Array in O(n)
  26. Find Two Unique Numbers from Array in O(n)
  27. Number Patterns & Finding Smallest Number
  28. First Unique Element in a Stream
  29. Flip Equivalent Binary Trees [TeachMint]
  30. Minimum Cost of Merging Files [Amazon]
  31. Minimum Distance for Truck to Deliver Order [Amazon]
  32. Longest Sequence of URLs
  33. Order Task for Given Dependencies
  34. Design Music Player
  35. Multilevel Parking System Design
  36. Minimum Coins Required
  37. Max Sum Subarray
  38. Max Avg Sum of Two Subsequences
  39. Merge Overlapping Intervals
  40. Longest Balanced Substring
  41. Longest Path in a Weighted Tree
  42. Generate Balanced Parentheses
  43. PostOrder Traversal Without Recursion

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