[SOLVED] How to improve the code to return the unpaired element


I am practising for an upcoming coding interview and here is one of my practice problems and my progress.

How can I improve the program and what is your advice?

Also, are there any cities that could help with improving my coding skills?


    A non-empty zero-indexed 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.
    Assume that:
    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.
    expected worst-case time complexity is O(N);
    expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).
    Elements of input arrays can be modified.


import java.util.*;

public class Solution {
    public int solution(int[] A) {
            int x;

        for(int i = 0; i < 7; i++)
             //create an integer array containing an odd number of elements of numbers ranging from 1 - 1,000,000
//for(int N = 1; N <= 1,000,000; N++)

            int N = 1;

            while(N > 1 && N <= 1000000)

                //check if N is odd then assign to the array               

                if(N != N/2)
                    A[i] = N;

            //check for any element not paired more than once

            if(A[i] != A[i++])
                x = A[i];
                return 0;

        //return unpaired elemnent
        return x;


Something like this should work, here I implemented it in a way where I test all ints it gets against the rest, and only return if there is a solution (note there has to be a default, maybe a better way to handle “no solutions”.

public class Solution {
    public int solution(int[] A) {

        boolean possibleSolution = true; // to return and properly break if not possible

        for(int i = 0; i < A.length; i++) // run for all ints
            possibleSolution = true; // set possible true, in case last one failed
            for(int j = 0; j < A.length; j++) // take all ints again (to compare to the rest
                if(A[i] == A[j] && i != j){ // note i escape comparing to itself
                    possibleSolution = false; // if there is a math it can't be this one
                    break; // break to save resources
            if(possibleSolution) // if it's the solution
                return A[i]; // return the current number (from the initial array as that is the reference number and the 2nd is for comparing)

        return 0; // return default

    public static void main(String[] args){
        Solution solution = new Solution(); // instance
        int[] ints = {9,3,9,3,9,7,9}; // new values
        System.out.println(solution.solution(ints)); // print the method after it was run

Note that adding the ints, is not included here unsure what types of values is needed

but simply add them and then pass the array, if multiple answers are possible, then instead of return add to a List<Integers> results = new ArrayList<>();, and after all i is run through return the resultsthis would be where the return 0; is at the moment.

Answered By – Mikenno

Answer Checked By – Timothy Miller (BugsFixing Admin)

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