Test results - Codility

Tasks Details

easy

1. StoneWall

Cover "Manhattan skyline" using the minimum number of rectangles.

100%

You are going to build a stone wall. The wall should be straight and N meters long, and its thickness should be constant; however, it should have different heights in different places. The height of the wall is specified by an array H of N positive integers. H[I] is the height of the wall from I to I+1 meters to the right of its left end. In particular, H[0] is the height of the wall's left end and H[N−1] is the height of the wall's right end.

The wall should be built of cuboid stone blocks (that is, all sides of such blocks are rectangular). Your task is to compute the minimum number of blocks needed to build the wall.

Write a function:

class Solution { public int solution(int[] H); }

that, given an array H of N positive integers specifying the height of the wall, returns the minimum number of blocks needed to build it.

For example, given array H containing N = 9 integers:

H[0] = 8 H[1] = 8 H[2] = 5 H[3] = 7 H[4] = 9 H[5] = 8 H[6] = 7 H[7] = 4 H[8] = 8

the function should return 7. The figure shows one possible arrangement of seven blocks.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [1..100,000];

each element of array H is an integer within the range [1..1,000,000,000].

Solution

Programming language used C#

Time spent on task 2 minutes

Notes

not defined yet

Code: 20:37:09 UTC, cs, verify, result: Passed

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using System;
// you can also use other imports, for example:
using System.Collections.Generic;

// you can write to stdout for debugging purposes, e.g.
// Console.WriteLine("this is a debug message");

class Solution {
    public int solution(int[] H)
    {
         int blocks = 0;
         var levels = new Stack<int>();

         for (int i = 0; i < H.Length; i++)
         {
            if (levels.Count == 0)
            {
               levels.Push(H[i]);
            }
            else
            {
               var lastLevel = levels.Peek();

               if (lastLevel < H[i])
               {
                  levels.Push(H[i]);
               }
               else if (lastLevel == H[i])
               {
                  // nothing to do
               }
               else // lastLevel > H[i]
               {
                  // keep popping levels until one is smaller than the current one
                  while (true)
                  {
                     levels.Pop();  // pop the last level
                     blocks++;      // increment the block counter

                     if (levels.Count == 0)
                     {
                        // nothing left to pop
                        levels.Push(H[i]);   // push current level
                        break;
                     }
                     // else, there are more levels in the stack

                     lastLevel = levels.Peek();

                     if (lastLevel < H[i])
                     {
                        // no need to pop-up any more levels
                        levels.Push(H[i]);   // push current level
                        break;
                     }
                     else if (lastLevel == H[i])
                     {
                        // no need to pop-up any more levels and no need to push a new level either
                        break;
                     }
                     // else, repeat the while loop
                  }
               }
            }
         }

         blocks += levels.Count;

         return blocks;
    }
}

Code: 20:37:15 UTC, cs, verify, result: Passed

using System;
// you can also use other imports, for example:
using System.Collections.Generic;

// you can write to stdout for debugging purposes, e.g.
// Console.WriteLine("this is a debug message");

class Solution {
    public int solution(int[] H)
    {
         int blocks = 0;
         var levels = new Stack<int>();

         for (int i = 0; i < H.Length; i++)
         {
            if (levels.Count == 0)
            {
               levels.Push(H[i]);
            }
            else
            {
               var lastLevel = levels.Peek();

               if (lastLevel < H[i])
               {
                  levels.Push(H[i]);
               }
               else if (lastLevel == H[i])
               {
                  // nothing to do
               }
               else // lastLevel > H[i]
               {
                  // keep popping levels until one is smaller than the current one
                  while (true)
                  {
                     levels.Pop();  // pop the last level
                     blocks++;      // increment the block counter

                     if (levels.Count == 0)
                     {
                        // nothing left to pop
                        levels.Push(H[i]);   // push current level
                        break;
                     }
                     // else, there are more levels in the stack

                     lastLevel = levels.Peek();

                     if (lastLevel < H[i])
                     {
                        // no need to pop-up any more levels
                        levels.Push(H[i]);   // push current level
                        break;
                     }
                     else if (lastLevel == H[i])
                     {
                        // no need to pop-up any more levels and no need to push a new level either
                        break;
                     }
                     // else, repeat the while loop
                  }
               }
            }
         }

         blocks += levels.Count;

         return blocks;
    }
}

Code: 20:37:18 UTC, cs, final, score: 100

using System;
// you can also use other imports, for example:
using System.Collections.Generic;

// you can write to stdout for debugging purposes, e.g.
// Console.WriteLine("this is a debug message");

class Solution {
    public int solution(int[] H)
    {
         int blocks = 0;
         var levels = new Stack<int>();

         for (int i = 0; i < H.Length; i++)
         {
            if (levels.Count == 0)
            {
               levels.Push(H[i]);
            }
            else
            {
               var lastLevel = levels.Peek();

               if (lastLevel < H[i])
               {
                  levels.Push(H[i]);
               }
               else if (lastLevel == H[i])
               {
                  // nothing to do
               }
               else // lastLevel > H[i]
               {
                  // keep popping levels until one is smaller than the current one
                  while (true)
                  {
                     levels.Pop();  // pop the last level
                     blocks++;      // increment the block counter

                     if (levels.Count == 0)
                     {
                        // nothing left to pop
                        levels.Push(H[i]);   // push current level
                        break;
                     }
                     // else, there are more levels in the stack

                     lastLevel = levels.Peek();

                     if (lastLevel < H[i])
                     {
                        // no need to pop-up any more levels
                        levels.Push(H[i]);   // push current level
                        break;
                     }
                     else if (lastLevel == H[i])
                     {
                        // no need to pop-up any more levels and no need to push a new level either
                        break;
                     }
                     // else, repeat the while loop
                  }
               }
            }
         }

         blocks += levels.Count;

         return blocks;
    }
}

Analysis summary

The solution obtained perfect score.

Analysis

Detected time complexity:

O(N)

▶

example

✔

▶

simple1

✔

▶

simple2

✔

▶

simple3

✔

▶

simple4

✔

▶

boundary_cases

✔

▶

medium1

✔

▶

medium2

✔

▶

medium3

✔

▶

medium4

✔

▶

large_piramid

✔

▶

large_increasing_decreasing

✔

▶

large_up_to_20

✔

▶

large_up_to_100

✔

▶

large_max

✔