Test results - Codility

Tasks Details

easy

1. Dominator

Find an index of an array such that its value occurs at more than half of indices in the array.

Task Score

100%

Correctness

100%

Performance

100%

An array A consisting of N integers is given. The dominator of array A is the value that occurs in more than half of the elements of A.

For example, consider array A such that

A[0] = 3 A[1] = 4 A[2] = 3 A[3] = 2 A[4] = 3 A[5] = -1 A[6] = 3 A[7] = 3

The dominator of A is 3 because it occurs in 5 out of 8 elements of A (namely in those with indices 0, 2, 4, 6 and 7) and 5 is more than a half of 8.

Write a function

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

that, given an array A consisting of N integers, returns index of any element of array A in which the dominator of A occurs. The function should return −1 if array A does not have a dominator.

For example, given array A such that

A[0] = 3 A[1] = 4 A[2] = 3 A[3] = 2 A[4] = 3 A[5] = -1 A[6] = 3 A[7] = 3

the function may return 0, 2, 4, 6 or 7, as explained above.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [0..100,000];

each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].

Solution

Programming language used C#

Time spent on task 10 minutes

Notes

not defined yet

Task timeline

Code: 07:52:10 UTC, cs, verify, result: Failed

show code in pop-up

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Lenght;
        int size =0;
        Stack<int> s = new Stack<int>;
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek(A[i]) != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

Compile error

Compilation failed: 1 error(s), 0 warnings
Solution.cs(13,37): error CS1525: Unexpected symbol `;', expecting `(', `[', or `{'

Code: 07:52:22 UTC, cs, verify, result: Failed

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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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Lenght;
        int size =0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek(A[i]) != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

Compile error

Compilation failed: 4 error(s), 0 warnings
Solution.cs(11,19): error CS1061: Type `int[]' does not contain a definition for `Lenght' and no extension method `Lenght' of type `int[]' could be found. Are you missing an assembly reference?
/opt/codility-mono/lib/mono/4.5/mscorlib.dll (Location of the symbol related to previous error)
Solution.cs(13,9): error CS0246: The type or namespace name `Stack' could not be found. Are you missing `System.Collections.Generic' using directive?
Solution.cs(20,17): error CS0841: A local variable `s' cannot be used before it is declared
Solution.cs(24,21): error CS0841: A local variable `s' cannot be used before it is declared

Code: 07:52:35 UTC, cs, verify, result: Failed

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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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Lenght;
        int size =0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek(A[i]) != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

Compile error

Compilation failed: 2 error(s), 0 warnings
Solution.cs(11,19): error CS1061: Type `int[]' does not contain a definition for `Lenght' and no extension method `Lenght' of type `int[]' could be found. Are you missing an assembly reference?
/opt/codility-mono/lib/mono/4.5/mscorlib.dll (Location of the symbol related to previous error)
Solution.cs(24,23): error CS1501: No overload for method `Peek' takes `1' arguments
/opt/codility-mono/lib/mono/4.5/System.dll (Location of the symbol related to previous error)

Code: 07:53:22 UTC, cs, verify, result: Failed

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek(A[i]) != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

Compile error

Compilation failed: 1 error(s), 0 warnings
Solution.cs(24,23): error CS1501: No overload for method `Peek' takes `1' arguments
/opt/codility-mono/lib/mono/4.5/System.dll (Location of the symbol related to previous error)

Code: 07:53:26 UTC, cs, verify, result: Failed

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek(A[i]) != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

Compile error

Compilation failed: 1 error(s), 0 warnings
Solution.cs(24,23): error CS1501: No overload for method `Peek' takes `1' arguments
/opt/codility-mono/lib/mono/4.5/System.dll (Location of the symbol related to previous error)

Code: 07:53:43 UTC, cs, verify, result: Failed

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek() != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

expand all Example tests

▶

example
example test

✘

WRONG ANSWER
got -1, but dominator exists, for example on position 6

0.065 s

WRONG ANSWER, got -1, but dominator exists, for example on position 6

Code: 07:55:59 UTC, cs, verify, result: Failed

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        int value=0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek() != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        if (size>0) candidate = s.Peek();
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return leader;
    }
}

Analysis

expand all Example tests

▶

example
example test

✘

WRONG ANSWER
got 3, but element is not a dominator, value 2 has only 1 occurences (n=8)

0.065 s

WRONG ANSWER, got 3, but element is not a dominator, value 2 has only 1 occurences (n=8)

Code: 07:56:43 UTC, cs, verify, result: Passed

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        int value=0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek() != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        if (size>0) candidate = s.Peek();
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return Array.IndexOf(A, leader);
    }
}

Analysis

expand all Example tests

▶

example
example test

✔

0.070 s

Code: 07:56:49 UTC, cs, verify, result: Passed

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        int value=0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek() != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        if (size>0) candidate = s.Peek();
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return Array.IndexOf(A, leader);
    }
}

Analysis

expand all Example tests

▶

example
example test

✔

0.060 s

Code: 07:56:52 UTC, cs, final, score: 100

show code in pop-up

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

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

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

class Solution {
    public int solution(int[] A) {
        // write your code in C# 6.0 with .NET 4.5 (Mono)
        int n = A.Length;
        int size =0;
        int value=0;
        Stack<int> s = new Stack<int>();
        
        for (int i=0; i<n; i++)
        {
            if(size ==0)
            {
                size +=1;
                s.Push(A[i]);
            }
            else
            {
                if (s.Peek() != A[i]) size -=1;
                else size +=1;
            }           
        }
        int candidate = -1;
        if (size>0) candidate = s.Peek();
        int count =0;
        int leader= -1;
        
        for (int i=0; i<n; i++)
        {
         if (A[i] == candidate) count +=1;
         if (count > n/2) leader = candidate;
        }
        
        return Array.IndexOf(A, leader);
    }
}

Analysis summary

The solution obtained perfect score.

Analysis

Detected time complexity:

O(N) or O(N*log(N))

expand all Example tests

▶

example
example test

✔

0.065 s

expand all Correctness tests

▶

small_nondominator
all different and all the same elements

✔

0.065 s

0.066 s

▶

small_half_positions
half elements the same, and half + 1 elements the same

✔

0.066 s

0.064 s

▶

small
small test

✔

0.066 s

▶

small_pyramid
decreasing and plateau, small

✔

0.065 s

▶

extreme_empty_and_single_item
empty and single element arrays

✔

0.065 s

0.066 s

▶

extreme_half1
array with exactly N/2 values 1, N even + [0,0,1,1,1]

✔

0.066 s

▶

extreme_half2
array with exactly floor(N/2) values 1, N odd + [0,0,1,1,1]

✔

0.066 s

▶

extreme_half3
array with exactly ceil(N/2) values 1 + [0,0,1,1,1]

✔

0.065 s

expand all Performance tests

▶

medium_pyramid
decreasing and plateau, medium

✔

0.069 s

▶

large_pyramid
decreasing and plateau, large

✔

0.102 s

▶

medium_random
random test with dominator, N = 10,000

✔

0.071 s

▶

large_random
random test with dominator, N = 100,000

✔

0.111 s