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Count Snow Units Captured between the Hills asked in GS [Coding Challenge]

Aniruddha Chaudhari/288/0
CodePython

Note: This coding challenge was asked in Goldman Sach coding round and in many other technical job interviews.

Given an array of non-negative integers representing the elevations from the vertical cross-section of a range of hills, determine how many units of snow could be captured between the hills.

Example: 

See the example array and elevation map below.

Output: In this example, 13 units of snow (*) could be captured.

This problem is similar to the “maximum level of water it can trap after the rain”.

Explanation with algorithm:

  • Create array left and save all the local current maxima while traversing from left to right.
  • Create an array right and save all the local current maxima while traversing from right to left.
  • find min(left[i], right[i]) - arr[i] for each element.
  • Cacualte the sum form resultant array.

Python Solution

We are implementing above algorithm using Python programming.

Prerequisite:

  • Python list
def computeSnowpack(arr):
    # Todo: Implement computeSnowpack

    len_arr = len(arr)
    left = [arr[0]]*len_arr
    left_max = arr[0]
    for i in range(1, len_arr):
        left_max = left_max if left_max>arr[i] else arr[i]
        left[i] = left_max
    
    right = [arr[-1]]*len_arr
    right_max = arr[-1]
    for i in range(len_arr-2, -1, -1):
        right_max = right_max if right_max>arr[i] else arr[i]
        right[i] = right_max

    sum = 0
    for i in range(len_arr) :
        sum += min(left[i], right[i]) - arr[i]

    return sum

def doTestsPass():
    """ Returns True if all tests pass. Otherwise returns False. """
    tests = [ 
      [[2, 1, 3, ], 1], 
      [[0,1,3,0,1,2,0,4,2,0,3,0], 13], 
      [[2,1,3,0,1,2,0,4,2,0,3,0], 14],
    ]

    for test in tests:
        if not (computeSnowpack(test[0]) == test[1]):
            return False
    return True

if __name__ == "__main__":
    if( doTestsPass() ):
        print( "All tests pass" )
    else:
        print( "Not all tests pass")

Complexity:

  • The time complexity of this algorithm is O(n).
  • The space complexity of this algorithm is O(n).

Similar coding challenges asked in Goldman Sachs

  • Special Elements in Matrix
  • Secure My Conversation by Encryption and Decryption

If you have any other solution or if you have any question, let’s discuss in the comment.

Python Interview Questions eBook

coding challengeGoldman SachsPython
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. Min Arrow to Burst Bubbles
  14. Min Cost to Paint All Houses [Amazon]
  15. HourGlass with Largest Sum
  16. Max Profit by Buying/Selling Stocks
  17. Hailstone Sequence
  18. Reverse String without affecting Special Characters
  19. Secure Conversation by Encry/Decry
  20. Special Elements in Matrix
  21. Next Greater No with Same set of Digits
  22. Smallest Subarray with Sum Greater than Given Number
  23. Group Anagrams
  24. Find Duplicates in Array in O(n)
  25. Find Two Unique Numbers from Array in O(n)
  26. Number Patterns & Finding Smallest Number
  27. First Unique Element in a Stream
  28. Flip Equivalent Binary Trees [TeachMint]
  29. Minimum Cost of Merging Files [Amazon]
  30. Minimum Distance for Truck to Deliver Order [Amazon]
  31. Order Task for Given Dependencies
  32. Multilevel Parking System Design
  33. Minimum Coins Required
  34. Max Sum Subarray
  35. Max Avg Sum of Two Subsequences
  36. Merge Overlapping Intervals
  37. Longest Balanced Subarray
  38. Longest Path in a Weighted Tree
  39. Generate Balanced Parentheses
  40. PostOrder Traversal Without Recursion

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