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AVAILABLE LESSONS:

Lesson 1

Iterations

Lesson 2

Arrays

Lesson 3

Time Complexity

Lesson 4

Counting Elements

Lesson 5

Prefix Sums

Lesson 6

Sorting

Lesson 7

Stacks and Queues

Lesson 8

Leader

Lesson 9

Maximum slice problem

Lesson 10

Prime and composite numbers

Lesson 11

Sieve of Eratosthenes

Lesson 12

Euclidean algorithm

Lesson 13

Fibonacci numbers

Lesson 14

Binary search algorithm

Lesson 15

Caterpillar method

Lesson 16

Greedy algorithms

Lesson 17

Dynamic programming

Lesson 90

Tasks from Indeed Prime 2015 challenge

Lesson 91

Tasks from Indeed Prime 2016 challenge

Lesson 92

Tasks from Indeed Prime 2016 College Coders challenge

Lesson 99

Future training

painless

Find value that occurs in odd number of elements.

Programming language:
Spoken language:

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

int solution(int A[], int N);

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

Copyright 2009–2018 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

int solution(vector<int> &A);

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

Copyright 2009–2018 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

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

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

Copyright 2009–2018 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

func Solution(A []int) int

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

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

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

function solution(A);

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

function solution(A)

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

int solution(NSMutableArray *A);

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

function solution(A: array of longint; N: longint): longint;

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

function solution($A);

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

sub solution { my (@A)=@_; ... }

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

def solution(A)

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

def solution(a)

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

object Solution { def solution(a: Array[Int]): Int }

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

public func solution(inout A : [Int]) -> Int

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

public func solution(_ A : inout [Int]) -> Int

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

给定一个非空数组 A，包含有 N 个整数，起始下标为 0。数组包含有奇数个元素，其中除了唯一一个元素之外，其他每个元素都可以与数组中另一个有相同值的元素配对。

比如，在下面这个数组中：

- 下标为 0 和 2 的元素的值是 9
- 下标为 1 和 3 的元素的值是 3
- 下标为 4 和 6 的元素的值是 9
- 下标为 5 的元素的值是 7，无法配对

写一个函数：

Private Function solution(A As Integer()) As Integer

对满足上述条件的数组 A，返回数组中无法配对的元素的值。

比如，给定以下数组：

函数应该返回 7，如上述解释。

假定:

- N is an odd integer within the range [1..1,000,000];
- 数组 A 每个元素是取值范围 [1..1,000,000,000] 内的 整数 ;
- all but one of the values in A occur an even number of times.

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:

- 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:

int solution(int A[], int N);

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:

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.

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:

- 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:

int solution(vector<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:

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.

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:

- 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:

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.

For example, in array A such that:

- 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:

func Solution(A []int) int

For example, given array A such that:

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.

For example, in array A such that:

- 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); }

For example, given array A such that:

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.

For example, in array A such that:

- 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:

function solution(A);

For example, given array A such that:

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.

For example, in array A such that:

- 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:

function solution(A)

For example, given array A such that:

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.

Note: All arrays in this task are zero-indexed, unlike the common Lua convention. You can use `#A` to get the length of the array A.

For example, in array A such that:

- 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:

int solution(NSMutableArray *A);

For example, given array A such that:

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.

For example, in array A such that:

- 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:

function solution(A: array of longint; N: longint): longint;

For example, given array A such that:

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.

For example, in array A such that:

- 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:

function solution($A);

For example, given array A such that:

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.

For example, in array A such that:

- 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:

sub solution { my (@A)=@_; ... }

For example, given array A such that:

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.

For example, in array A such that:

- 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:

def solution(A)

For example, given array A such that:

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.

For example, in array A such that:

- 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:

def solution(a)

For example, given array A such that:

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.

For example, in array A such that:

- 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:

object Solution { def solution(a: Array[Int]): Int }

For example, given array A such that:

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.

For example, in array A such that:

- 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:

public func solution(inout A : [Int]) -> Int

For example, given array A such that:

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.

For example, in array A such that:

- 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:

public func solution(_ A : inout [Int]) -> Int

For example, given array A such that:

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.

For example, in array A such that:

- 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:

Private Function solution(A As Integer()) As Integer

For example, given array A such that:

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.

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