//

// leetcode_1_Two Sum.swift

// fight

//

// Created by 이재은 on 2020/11/25.

// Copyright © 2020 jaeeun. All rights reserved.

//

import Foundation

//LeetCode 1. Two Sum

// 주어진 nums 배열에서 2개의 원소를 더해 target이 될 수 있는 수의 배열 인덱스 구하기

//Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

//

//You may assume that each input would have exactly one solution, and you may not use the same element twice.

//

//You can return the answer in any order.

//

//

//

//Example 1:

//

//Input: nums = [2,7,11,15], target = 9

//Output: [0,1]

//Output: Because nums[0] + nums[1] == 9, we return [0, 1].

//Example 2:

//

//Input: nums = [3,2,4], target = 6

//Output: [1,2]

//Example 3:

//

//Input: nums = [3,3], target = 6

//Output: [0,1]

//

//

//Constraints:

//

//2 <= nums.length <= 10^3

//-10^9 <= nums[i] <= 10^9

//-10^9 <= target <= 10^9

//Only one valid answer exists.

// 풀이 1

func twoSum(_ nums: [Int], _ target: Int) -> [Int] {

var result = [Int]()

for (index, n) in nums.enumerated() {

for j in index + 1..<nums.count {

if n + nums[j] == target {

result.append(index)

result.append(j)

break

}

}

}

return result

}

// 풀이 2

func twoSum(_ nums: [Int], _ target: Int) -> [Int] {

let numsSet = Set(nums)

for (index, num) in nums.enumerated() {

let complement = target - num

if numsSet.contains(complement) {

let complementIndex = nums.lastIndex(of: complement)!

if complementIndex != index {

return [index, complementIndex]

}

}

}

return []

}

// 풀이 3

func twoSum(_ nums: [Int], _ target: Int) -> [Int] {

var dict: [Int: Int] = [:]

for (i, n) in nums.enumerated() {

if let index = dict[target - n] {

return [index, i]

}

dict[n] = i

}

return []

}

print(twoSum([2,7,11,15], 9)) // [0, 1]

print(twoSum([3,2,4], 6)) // [1,2]

print(twoSum([3,3], 6)) // [0, 1]

print(twoSum([-1,-2,-3,-4,-5], -8)) // [2,4]

print(twoSum([0,4,3,0], 0)) // [0,3]