Find the value that occurs in an odd number of elements.
- Difficulty Level: Easy
- Question URL: https://app.codility.com/programmers/lessons/2-arrays/odd_occurrences_in_array/
- Time Complexity:
Question:
A non-empty array A consisting of N integers is given. The array contains an odd number of elements, and each element of the array can be paired with another element that has the same value, except for one element that is left unpaired.
For example, in array A such that:
A[0] = 9 A[1] = 3 A[2] = 9 A[3] = 3 A[4] = 9 A[5] = 7 A[6] = 9
- the elements at indexes 0 and 2 have value 9,
- the elements at indexes 1 and 3 have value 3,
- the elements at indexes 4 and 6 have value 9,
- the element at index 5 has value 7 and is unpaired.
Write a function:
class Solution { public int solution(int[] A); }
that, given an array A consisting of N integers fulfilling the above conditions, returns the value of the unpaired element.
For example, given array A such that:
A[0] = 9 A[1] = 3 A[2] = 9 A[3] = 3 A[4] = 9 A[5] = 7 A[6] = 9
the function should return 7, as explained in the example above.
Write an efficient algorithm for the following assumptions:
- N is an odd integer within the range [1..1,000,000];
- each element of array A is an integer within the range [1..1,000,000,000];
- all but one of the values in A occur an even number of times.
Solution:
Solution to Codility's Odd Occurrences In Array problem which is from the Codility Lesson 2: Arrays and, is solved in Java 8 with 100% performance and correctness scores. The goal here is to find the value that occurs in an odd number of elements. You can find the question of this OddOccurrencesInArray problem in the Codility website.
package Codility.Lesson2;
import java.util.*;
public class OddOccurrencesInArray {
public static void main(String[] args) {
int[] A = { 9, 3, 9, 3, 9, 7, 9 };
Integer result = solution(A);
System.out.println(result);
}
public static Integer solution(int[] A) {
// write your code in Java SE 8
HashMap <Integer, Boolean> occurMap = new HashMap<Integer, Boolean>();
for (int i = 0; i < A.length; i++) {
if (occurMap.containsKey(A[i])) {
if(occurMap.get(A[i])){
occurMap.put(A[i], false);
}else {
occurMap.put(A[i], true);
}
}else {
occurMap.put(A[i], false);
}
}
for (Map.Entry<Integer, Boolean> set : occurMap.entrySet()) {
if (set.getValue() == false) {
return set.getKey();
}
}
throw new RuntimeException("No value that occurs in odd number of elements.");
}
}