Test results - Codility

Tasks Details

easy

1. PermCheck

Check whether array A is a permutation.

100%

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].

Solution

Programming language used Java 8

Time spent on task 1 minutes

Notes

not defined yet

Task timeline

Code: 16:53:17 UTC, java, verify, result: Passed

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// 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) {
        Set<Integer> nums = new HashSet<Integer>();
        for (int i = 1; i <= A.length; i++) {
            nums.add(i);
        }

        for (int a : A) {
            if (!nums.contains(a)) {
                return 0;
            } else {
                nums.remove(a);
            }
        }
        return nums.isEmpty() ? 1 : 0;
    }
}

Analysis

▶

example1
the first example test

✔

▶

example2
the second example test

✔

Code: 16:53:23 UTC, java, 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

// 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) {
        Set<Integer> nums = new HashSet<Integer>();
        for (int i = 1; i <= A.length; i++) {
            nums.add(i);
        }

        for (int a : A) {
            if (!nums.contains(a)) {
                return 0;
            } else {
                nums.remove(a);
            }
        }
        return nums.isEmpty() ? 1 : 0;
    }
}

Analysis summary

The solution obtained perfect score.

Analysis

Detected time complexity:

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

▶

example1
the first example test

✔

▶

example2
the second example test

✔

▶

extreme_min_max
single element with minimal/maximal value

✔

▶

single
single element

✔

▶

double
two elements

✔

▶

antiSum1
total sum is correct, but it is not a permutation, N <= 10

✔

▶

small_permutation
permutation + one element occurs twice, N = ~100

✔

▶

permutations_of_ranges
permutations of sets like [2..100] for which the anwsers should be false

✔

▶

medium_permutation
permutation + few elements occur twice, N = ~10,000

✔

▶

antiSum2
total sum is correct, but it is not a permutation, N = ~100,000

✔

▶

large_not_permutation
permutation + one element occurs three times, N = ~100,000

✔

▶

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

✔

▶

extreme_values
all the same values, N = ~100,000

✔

▶

various_permutations
all sequences are permutations

✔