Java solution to Codility MissingInteger problem (Lesson 4 – Counting Elements) which scored 100%. The problem is to find the smallest positive integer that does not occur in a given array. The main strategy is to use two java.util.TreeSets, which order their elements: 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.
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import java.util.Set;
import java.util.TreeSet;
public class MissingInteger {
public int solution(int[] A) {
Set testedSet = new TreeSet();
Set perfectSet = new TreeSet();
for(int i=0; i<A.length; i++) {
testedSet.add(A[i]); //convert array to set to get rid of duplicates, order int's
perfectSet.add(i+1); //create perfect set so can find missing int
}
for(int current : perfectSet) {
if(!testedSet.contains(current)) {
return current;
}
}
if(perfectSet.size() == testedSet.size()) {
return perfectSet.size() + 1; //e.g. {1, 2, 3} should return 4
}
return 1; //default - e.g. if A array has negative values or just a single positive value like 10
}
}
TestNG test cases for this problem which all passed:
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import org.testng.Assert;
import org.testng.annotations.*;
import com.codility.lesson04.countingelements.MissingInteger;
public class MissingIntegersTests {
private MissingInteger solution;
@BeforeTest
public void setUp() {
solution = new MissingInteger();
}
@DataProvider(name = "test1")
public Object [][] createData1() {
return new Object [][] {
new Object [] { new int [] { 1, 3, 6, 4, 1, 2 }, 5 },
new Object [] { new int [] { 1, 3, 6, 4, 1, 2, 5 }, 7 },
new Object [] { new int [] { 1, 2, 3 }, 4 },
new Object [] { new int [] { -1,-3 }, 1 },
new Object [] { new int [] { -1,-3, 2 }, 1 },
new Object [] { new int [] { -1,-3, 1 }, 2 },
new Object [] { new int [] { 0 }, 1 },
new Object [] { new int [] { -1000000 }, 1 },
new Object [] { new int [] { -1000000, 1 }, 2 },
new Object [] { new int [] { 1000000 }, 1 },
new Object [] { new int [] { 999999, 999998, 1000000 }, 1 },
new Object [] { new int [] { 1, 3, 999999, 999998, 1000000 }, 2 },
};
}
@Test(dataProvider = "test1")
public void verifySolution(int [] pA, int pExpected) {
Assert.assertEquals(solution.solution(pA), pExpected);
}
}