将来的工作需要用到Swift，可是看语法什么的好无聊啊，最近又恰好发现leetCode支持Swift，以前又没刷过leetCode，于是就借着这个机会，边刷边学学Swift。
题目： Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
example:
Given nums = [2, 7, 11, 15], target = 9, Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1]
题目本身没什么意思，要在时间复杂度o(n)内求解，主要就是利用map记录一下value-index。这里主要是学习一下Swift的语法，下面是leetCode上别人的solution。关键的语法点就是数组，字典的使用，变量的定义，if-else。
class Solution { func twoSum(_ nums: [Int], _ target: Int) -> [Int] { var selectedIndices = [Int:Int]() for (index, element) in nums.enumerated() { selectedIndices[element] = index } for (index, element) in nums.enumerated() { let compliment = target - element if let selectedIndex = selectedIndices[compliment] { if selectedIndex != index { return [index, selectedIndex] } } } return [] } }