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Tasks Details
easy
Check whether array A is a permutation.
Task Score
100%
Correctness
100%
Performance
100%

Task description

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

A permutation is a sequence containing each element from 1 to N once, and only once.

For example, array A such that:

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

is a permutation, but array A such that:

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

is not a permutation, because value 2 is missing.

The goal is to check whether array A is a permutation.

Write a function:

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

that, given an array A, returns 1 if array A is a permutation and 0 if it is not.

For example, given array A such that:

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

the function should return 1.

Given array A such that:

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

the function should return 0.

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..1,000,000,000].
Copyright 2009–2025 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used Java 8
Time spent on task 1 minutes
Notes
not defined yet
Task timeline
08:52:38
08:52:55

Away from Codility tab

0%

Code: 08:52:54 UTC, java, final, score:  100
// you can also use imports, for example:
// import java.util.*;

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

class Solution {
    public int solution(int[] A) {
        java.util.Arrays.sort(A);
        for (int i = 0; i < A.length; i++) {
            if (A[i] == i + 1) continue;
            else return 0;
        }

        return 1;
    }
}
Analysis summary

The solution obtained perfect score.

Analysis
Detected time complexity:
O(N) or O(N * log(N))
expand all Example tests
example1
the first example test
OK
example2
the second example test
OK
expand all Correctness tests
extreme_min_max
single element with minimal/maximal value
OK
single
single element
OK
double
two elements
OK
antiSum1
total sum is correct, but it is not a permutation, N <= 10
OK
small_permutation
permutation + one element occurs twice, N = ~100
OK
permutations_of_ranges
permutations of sets like [2..100] for which the anwsers should be false
OK
expand all Performance tests
medium_permutation
permutation + few elements occur twice, N = ~10,000
OK
antiSum2
total sum is correct, but it is not a permutation, N = ~100,000
OK
large_not_permutation
permutation + one element occurs three times, N = ~100,000
OK
large_range
sequence 1, 2, ..., N, N = ~100,000
OK
extreme_values
all the same values, N = ~100,000
OK
various_permutations
all sequences are permutations
OK