Tasks Details
easy
Find the missing element in a given permutation.
Task Score
100%
Correctness
100%
Performance
100%
An array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.
Your goal is to find that missing element.
Write a function:
class Solution { public int solution(int[] A); }
that, given an array A, returns the value of the missing element.
For example, given array A such that:
A[0] = 2 A[1] = 3 A[2] = 1 A[3] = 5the function should return 4, as it is the missing element.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [0..100,000];
- the elements of A are all distinct;
- each element of array A is an integer within the range [1..(N + 1)].
Copyright 2009–2025 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used C#
Time spent on task 3 minutes
Notes
not defined yet
Code: 15:58:51 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[] A)
{
long sumMax=((2L+A.Length)*(A.Length+1L))/2L;
long sum=0L;
for(int i=0;i<A.Length;i++)
{
sum+=A[i];
}
return (int)(sumMax-sum);
}
}
Analysis
Code: 15:58:58 UTC,
cs,
verify,
result: Failed
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[] A)
{
long sumMax=((2L+A.LengthL)*(A.Length+1L))/2L;
long sum=0L;
for(int i=0;i<A.Length;i++)
{
sum+=A[i];
}
return (int)(sumMax-sum);
}
}
Analysis
Compile error
Compilation failed: 1 error(s), 0 warnings Solution.cs(12,28): error CS1061: Type `int[]' does not contain a definition for `LengthL' and no extension method `LengthL' 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)
Code: 16:00:49 UTC,
cs,
verify,
result: Failed
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[] A)
{
long N=A.Length+1;
long total = N*(N+1)/2;
long sum=0L;
for(int i=0;i<A.Length;i++)
{
sum+=A[i];
}
return (int)(sumMax-sum);
}
}
Analysis
Compile error
Compilation failed: 1 error(s), 0 warnings Solution.cs(21,22): error CS0103: The name `sumMax' does not exist in the current context
Code: 16:00:59 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[] A)
{
long N=A.Length+1;
long total = N*(N+1)/2;
long sum=0L;
for(int i=0;i<A.Length;i++)
{
sum+=A[i];
}
return (int)(total-sum);
}
}
Analysis
Code: 16:01:03 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[] A)
{
long N=A.Length+1;
long total = N*(N+1)/2;
long sum=0L;
for(int i=0;i<A.Length;i++)
{
sum+=A[i];
}
return (int)(total-sum);
}
}
Analysis
Code: 16:01:05 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[] A)
{
long N=A.Length+1;
long total = N*(N+1)/2;
long sum=0L;
for(int i=0;i<A.Length;i++)
{
sum+=A[i];
}
return (int)(total-sum);
}
}Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N) or O(N * log(N))
expand all
Correctness tests
1.
0.060 s
OK
2.
0.061 s
OK
1.
0.060 s
OK
2.
0.060 s
OK
1.
0.061 s
OK
2.
0.060 s
OK
1.
0.061 s
OK
2.
0.060 s
OK
3.
0.060 s
OK
1.
0.061 s
OK
expand all
Performance tests
1.
0.063 s
OK
1.
0.064 s
OK
1.
0.096 s
OK
2.
0.078 s
OK
3.
0.078 s
OK
1.
0.096 s
OK
1.
0.082 s
OK