Test results - Codility

Tasks Details

easy

1. EquiLeader

Find the index S such that the leaders of the sequences A[0], A[1], ..., A[S] and A[S + 1], A[S + 2], ..., A[N - 1] are the same.

100%

A non-empty array A consisting of N integers is given.

The leader of this array is the value that occurs in more than half of the elements of A.

An equi leader is an index S such that 0 ≤ S < N − 1 and two sequences A[0], A[1], ..., A[S] and A[S + 1], A[S + 2], ..., A[N − 1] have leaders of the same value.

For example, given array A such that:

A[0] = 4 A[1] = 3 A[2] = 4 A[3] = 4 A[4] = 4 A[5] = 2

we can find two equi leaders:

0, because sequences: (4) and (3, 4, 4, 4, 2) have the same leader, whose value is 4.

2, because sequences: (4, 3, 4) and (4, 4, 2) have the same leader, whose value is 4.

The goal is to count the number of equi leaders.

Write a function:

Private Function solution(A As Integer()) As Integer

that, given a non-empty array A consisting of N integers, returns the number of equi leaders.

For example, given:

A[0] = 4 A[1] = 3 A[2] = 4 A[3] = 4 A[4] = 4 A[5] = 2

the function should return 2, as explained above.

Write an efficient algorithm for the following assumptions:

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

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

Solution

Programming language used Visual Basic

Time spent on task 4 minutes

Notes

not defined yet

Task timeline

Code: 22:57:12 UTC, vb, verify, result: Failed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

' you can use Console.WriteLine for debugging purposes, e.g.
' Console.WriteLine("this is a debug message")

Private Function solution(A As Integer()) As Integer
    ' write your code in VB.NET 4.0
    Dim result As Integer = 0
        Dim i, ladderVal, LadderCount, size, valCount As Integer
        ladderVal = 0
        LadderCount = 0
        size = A.Length
        If size > 0 Then


            For i = 1 To size - 1
                If LadderCount = 0 Then
                    LadderCount += 1
                    ladderVal = A(i)
                Else
                    If A(i) = ladderVal Then
                        LadderCount += 1
                    Else
                        LadderCount -= 1
                    End If
                End If
            Next
            valCount = 0
            For i = 0 To size - 1
                If A(i) = ladderVal Then
                    valCount += 1
                End If
            Next
            If valCount <= size / 2 Then
                result = 0
            Else
                LadderCount = 0
                For i = 0 To size - 1
                    If A(i) = ladderVal Then
                        valCount -= 1
                        LadderCount += 1
                    End If
                    If LadderCount > (LadderCount + 1) / 2 And (valCount > (size - (i + 1)) / 2) Then
                        result += 1
                    End If
                Next
            End If
        End If
        Return result
End Function

Analysis

▶

example
example test

✘

WRONG ANSWER
got 1 expected 2

Code: 23:00:29 UTC, vb, verify, result: Passed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

' you can use Console.WriteLine for debugging purposes, e.g.
' Console.WriteLine("this is a debug message")

Private Function solution(A As Integer()) As Integer
    ' write your code in VB.NET 4.0
    Dim result As Integer = 0
        Dim i, ladderVal, LadderCount, size, valCount As Integer
        ladderVal = 0
        LadderCount = 0
        size = A.Length
        If size > 0 Then


            For i = 1 To size - 1
                If LadderCount = 0 Then
                    LadderCount += 1
                    ladderVal = A(i)
                Else
                    If A(i) = ladderVal Then
                        LadderCount += 1
                    Else
                        LadderCount -= 1
                    End If
                End If
            Next
            valCount = 0
            For i = 0 To size - 1
                If A(i) = ladderVal Then
                    valCount += 1
                End If
            Next
            If valCount <= size / 2 Then
                result = 0
            Else
                LadderCount = 0
                For i = 0 To size - 1
                    If A(i) = ladderVal Then
                        valCount -= 1
                        LadderCount += 1
                    End If
                    If LadderCount > (i + 1) / 2 And (valCount > (size - (i + 1)) / 2) Then
                        result += 1
                    End If
                Next
            End If
        End If
        Return result
End Function

Analysis

▶

example
example test

✔

Code: 23:00:46 UTC, vb, verify, result: Passed

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

' you can use Console.WriteLine for debugging purposes, e.g.
' Console.WriteLine("this is a debug message")

Private Function solution(A As Integer()) As Integer
    ' write your code in VB.NET 4.0
    Dim result As Integer = 0
        Dim i, ladderVal, LadderCount, size, valCount As Integer
        ladderVal = 0
        LadderCount = 0
        size = A.Length
        If size > 0 Then


            For i = 1 To size - 1
                If LadderCount = 0 Then
                    LadderCount += 1
                    ladderVal = A(i)
                Else
                    If A(i) = ladderVal Then
                        LadderCount += 1
                    Else
                        LadderCount -= 1
                    End If
                End If
            Next
            valCount = 0
            For i = 0 To size - 1
                If A(i) = ladderVal Then
                    valCount += 1
                End If
            Next
            If valCount <= size / 2 Then
                result = 0
            Else
                LadderCount = 0
                For i = 0 To size - 1
                    If A(i) = ladderVal Then
                        valCount -= 1
                        LadderCount += 1
                    End If
                    If LadderCount > (i + 1) / 2 And (valCount > (size - (i + 1)) / 2) Then
                        result += 1
                    End If
                Next
            End If
        End If
        Return result
End Function

Analysis

▶

example
example test

✔

Code: 23:00:51 UTC, vb, final, score: 100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

' you can use Console.WriteLine for debugging purposes, e.g.
' Console.WriteLine("this is a debug message")

Private Function solution(A As Integer()) As Integer
    ' write your code in VB.NET 4.0
    Dim result As Integer = 0
        Dim i, ladderVal, LadderCount, size, valCount As Integer
        ladderVal = 0
        LadderCount = 0
        size = A.Length
        If size > 0 Then


            For i = 1 To size - 1
                If LadderCount = 0 Then
                    LadderCount += 1
                    ladderVal = A(i)
                Else
                    If A(i) = ladderVal Then
                        LadderCount += 1
                    Else
                        LadderCount -= 1
                    End If
                End If
            Next
            valCount = 0
            For i = 0 To size - 1
                If A(i) = ladderVal Then
                    valCount += 1
                End If
            Next
            If valCount <= size / 2 Then
                result = 0
            Else
                LadderCount = 0
                For i = 0 To size - 1
                    If A(i) = ladderVal Then
                        valCount -= 1
                        LadderCount += 1
                    End If
                    If LadderCount > (i + 1) / 2 And (valCount > (size - (i + 1)) / 2) Then
                        result += 1
                    End If
                Next
            End If
        End If
        Return result
End Function

Analysis summary

The solution obtained perfect score.

Analysis

Detected time complexity:

O(N)

▶

example
example test

✔

▶

single
single element

✔

▶

double
two elements

✔

▶

simple
simple test

✔

▶

small_random
small random test with two values, length = ~100

✔

▶

small
random + 200 * [MIN_INT] + random ,length = ~300

✔

▶

large_random
large random test with two values, length = ~50,000

✔

▶

large
random(0,1) + 50000 * [0] + random(0, 1), length = ~100,000

✔

▶

large_range
1, 2, ..., N, length = ~100,000

✔

▶

extreme_large
all the same values

✔