//

// leetcode_136_Single Number.swift

// fight

//

// Created by 이재은 on 2020/11/27.

// Copyright © 2020 jaeeun. All rights reserved.

//

import Foundation

// LeetCode 136. Single Number

// 주어진 배열에서 하나의 숫자를 빼고 나머지는 모두 2개씩 들어있음

// 개수가 하나인 원소를 구하기

//Given a non-empty array of integers nums, every element appears twice except for one. Find that single one.

//

//Follow up: Could you implement a solution with a linear runtime complexity and without using extra memory?

//

//

//Example 1:

//

//Input: nums = [2,2,1]

//Output: 1

//Example 2:

//

//Input: nums = [4,1,2,1,2]

//Output: 4

//Example 3:

//

//Input: nums = [1]

//Output: 1

//

//Constraints:

//

//1 <= nums.length <= 3 * 10^4

//-3 * 10^4 <= nums[i] <= 3 * 10^4

//Each element in the array appears twice except for one element which appears only once.

// 풀이 1

func singleNumber(_ nums: [Int]) -> Int {

var numCount = [Int: Int]()

for n in nums {

numCount[n, default: 0] += 1

}

return numCount.filter { $0.value == 1 }.keys.compactMap { Int($0) }.first!

}

// 풀이 2

func singleNumber(_ nums: [Int]) -> Int {

nums.reduce(0, ^)

}

// 풀이 3

func SingleNumber(_ nums: [Int]) -> Int {

let doubleSumNumsSet = 2 * Set(nums).reduce(0, +)

let sumNums = nums.reduce(0, +)

return doubleSumNumsSet - sumNums

}

// 풀이 4

func singleNumber(_ nums: [Int]) -> Int {

var numsSet = Set<Int>()

for n in nums {

if numsSet.contains(n) {

numsSet.remove(n)

} else {

numsSet.insert(n)

}

}

return numsSet.first!

}

print(singleNumber([1])) // 1

print(singleNumber( [4,1,2,1,2])) // 4

print(singleNumber([2,2,1])) // 1