## The challenge#

You are given an odd-length array of integers, in which all of them are the same, except for one single number.

Complete the method which accepts such an array, and returns that single different number.

The input array will always be valid! (odd-length >= 3)

## Examples#

``````[1, 1, 2] ==> 2
[17, 17, 3, 17, 17, 17, 17] ==> 3
``````

## The solution in Java code#

Option 1:

``````import java.util.*;

class Solution {
static int stray(int[] numbers) {
Map<Integer, Integer> map = new HashMap<>();

for (int i=0; i<numbers.length; i++) {
Integer def = map.getOrDefault(numbers[i], 0);
map.put(numbers[i], ++def);
}

for(Integer key : map.keySet()) {
System.out.println(key);
System.out.println(map.get(key));
if (map.get(key)==1) return key;
}

return 0;
}
}
``````

Option 2:

``````class Solution {
static int stray(int[] numbers) {
if (numbers[0] != numbers[1] && numbers[0] != numbers[2]) return numbers[0];
for (int i : numbers) if (i != numbers[0]) return i;
return 0;
}
}
``````

Option 3:

``````import java.util.Arrays;

class Solution {
static int stray(int[] numbers) {
return Arrays.stream(numbers).reduce(0, (a, b) -> a ^ b);
}
}
``````

## Test cases to validate our solution#

``````import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class SolutionTest {

@Test
public void simpleArray1() {
assertEquals(2, getActualFor(1, 1, 2));
}

@Test
public void simpleArray2() {
assertEquals(3, getActualFor(17, 17, 3, 17, 17, 17, 17));
}

@Test
public void firstItem() {
assertEquals(8, getActualFor(8, 1, 1, 1, 1, 1, 1));
}

@Test
public void lastItem() {
assertEquals(0, getActualFor(1, 1, 1, 1, 1, 1, 0));
}

@Test
public void middleItem() {
assertEquals(7, getActualFor(0, 0, 0, 7, 0, 0, 0));
}

@Test
public void fifthItem() {
assertEquals(-6, getActualFor(-21, -21, -21, -21, -6, -21, -21));
}

@Test
public void randomSmallArray() {
int strayNumber = SolutionHelper.randomInt(-10000, 10000);
int[] array = SolutionHelper.validRandomArray(101, strayNumber);
assertEquals(strayNumber, getActualFor(array));
}

@Test
public void randomBigArray() {
int strayNumber = SolutionHelper.randomInt(-10000, 10000);
int[] array = SolutionHelper.validRandomArray(15273, strayNumber);
assertEquals(strayNumber, getActualFor(array));
}

private int getActualFor(int... numbers) {
return Solution.stray(numbers);
}
}
``````