PermCheck – Codility – Solution

Java solution to Codility PermCheck (Permuation Check) problem (Lesson 4 – Counting Elements) which scored 100%. The problem is to check if the given array is a permutation. The main strategy is to use two java.util.HashSets: 1) a perfect set and 2) the actual set and check for the missing element in the actual set that exists in the perfect set.

[cc lang="java" escaped="true"]
package com.codility.lesson04.countingelements;

import java.util.HashSet;
import java.util.Set;

public class PermutationCheck {
	public int solution(int[] A) {
		Set testedSet = new HashSet();
		Set perfectSet = new HashSet();
		
		for(int i=0; i<A.length; i++) {
			testedSet.add(A[i]);
			perfectSet.add(i+1);
		}
		
		for(int current : perfectSet) {
			//as soon as find 1 element missing return false
			if(!testedSet.contains(current)) return 0;
		}
		return 1;
	}
}
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TestNG test cases for this problem which all passed:

[cc lang="java" escaped="true"]
package test.com.codility.lesson04.countingelements;
import org.testng.Assert;
import org.testng.annotations.*;

import com.codility.lesson04.countingelements.PermutationCheck;

public class PermutationCheckTests {
	private PermutationCheck solution;
	
	@BeforeTest
	public void setUp() {
		solution = new PermutationCheck();
	}

	@DataProvider(name = "test1")
	public Object [][] createData1() {
		return new Object [][] {
			new Object [] { new int [] {                1 }, 1 },
			new Object [] { new int [] {                2 }, 0 },
			new Object [] { new int [] {             1, 2 }, 1 },
			new Object [] { new int [] {             2, 2 }, 0 },
			new Object [] { new int [] {          1, 3, 2 }, 1 },
			new Object [] { new int [] {          1, 3, 3 }, 0 },
			new Object [] { new int [] {       4, 1, 3, 2 }, 1 },
			new Object [] { new int [] {          4, 1, 3 }, 0 },
			new Object [] { new int [] {    1, 3, 5, 4, 2 }, 1 },
			new Object [] { new int [] { 1, 3, 6, 4, 1, 2 }, 0 },
			new Object [] { new int [] { 1, 3, 5, 4, 6, 2 }, 1 },
			new Object [] { new int [] {          1000000 }, 0 },
			new Object [] { new int [] {       1, 1000000 }, 0 },
		};
	}

	@Test(dataProvider = "test1")
	public void verifySolution(int [] pA, int pExpected) {
		Assert.assertEquals(solution.solution(pA), pExpected);
	}
}
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