TwoSumII.swift

//
//  TwoSumII.swift
//  LeetCode.swift
//
//  Created by 叶帆 on 2020/3/8.
//  Copyright © 2020 Suzhou Coryphaei Information&Technology Co., Ltd. All rights reserved.
//

/**
 Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.

 The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2.

 Note:

 Your returned answers (both index1 and index2) are not zero-based.
 You may assume that each input would have exactly one solution and you may not use the same element twice.
 Example:

 Input: numbers = [2,7,11,15], target = 9
 Output: [1,2]
 Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.
 =====
 给定一个已按照升序排列 的有序数组，找到两个数使得它们相加之和等于目标数。

 函数应该返回这两个下标值 index1 和 index2，其中 index1 必须小于 index2。

 说明:

 返回的下标值（index1 和 index2）不是从零开始的。
 你可以假设每个输入只对应唯一的答案，而且你不可以重复使用相同的元素。
 示例:

 输入: numbers = [2, 7, 11, 15], target = 9
 输出: [1,2]
 解释: 2 与 7 之和等于目标数 9 。因此 index1 = 1, index2 = 2 。
 */

import Foundation

class Solution {
    func twoSum(_ numbers: [Int], _ target: Int) -> [Int] {
        var i = 0
        var j = numbers.count - 1
        while i < j {
            let sum = numbers[i] + numbers[j]
            if sum == target {
                return [i+1, j+1]
            }
            if sum < target {
                i += 1
            } else {
                j -= 1
            }
        }
        return []
    }
}