Tasks Details
medium
Find the smallest positive integer that does not occur in a given sequence.
Task Score
100%
Correctness
100%
Performance
100%
This is a demo task.
Write a function:
class Solution { public int solution(int[] A); }
that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.
For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.
Given A = [1, 2, 3], the function should return 4.
Given A = [−1, −3], the function should return 1.
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 [−1,000,000..1,000,000].
Copyright 2009–2025 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used Java 21
Time spent on task 25 minutes
Notes
not defined yet
Code: 04:24:42 UTC,
java,
autosave
Code: 04:49:32 UTC,
java,
verify,
result: Passed
// 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> set = new HashSet<Integer>();
for (int i = 0; i < A.length; i++) {
set.add(A[i]);
}
int max = 0, missing = -1;
for (int i = 0; i < A.length; i++) {
max = i + 1;
if (!set.contains(i + 1)) {
missing = i + 1;
break;
}
}
return missing == -1 ? max + 1 : missing;
}
}
Analysis
Code: 04:49:38 UTC,
java,
verify,
result: Passed
// 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> set = new HashSet<Integer>();
for (int i = 0; i < A.length; i++) {
set.add(A[i]);
}
int max = 0, missing = -1;
for (int i = 0; i < A.length; i++) {
max = i + 1;
if (!set.contains(i + 1)) {
missing = i + 1;
break;
}
}
return missing == -1 ? max + 1 : missing;
}
}
Analysis
Code: 04:49:42 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) {
Set<Integer> set = new HashSet<Integer>();
for (int i = 0; i < A.length; i++) {
set.add(A[i]);
}
int max = 0, missing = -1;
for (int i = 0; i < A.length; i++) {
max = i + 1;
if (!set.contains(i + 1)) {
missing = i + 1;
break;
}
}
return missing == -1 ? max + 1 : missing;
}
}
Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N) or O(N * log(N))
expand all
Correctness tests
1.
0.004 s
OK
2.
0.004 s
OK
3.
0.008 s
OK
4.
0.004 s
OK
1.
0.004 s
OK
2.
0.004 s
OK
3.
0.004 s
OK
1.
0.004 s
OK
2.
0.008 s
OK
1.
0.004 s
OK
2.
0.008 s
OK
1.
0.004 s
OK
expand all
Performance tests
1.
0.036 s
OK
2.
0.032 s
OK
3.
0.048 s
OK
1.
0.388 s
OK
1.
0.508 s
OK
2.
0.460 s
OK
1.
0.264 s
OK