[Swift]LeetCode167. 兩數之和 II - 輸入有序數組 | Two Sum II - Input array is sorted

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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.

---

給定一個已按照升序排列 的有序數組，找到兩個數使得它們相加之和等於目標數。

函數應該返回這兩個下標值 index1 和 index2，其中 index1 必須小於 index2。

說明:

• 返回的下標值（index1 和 index2）不是從零開始的。
• 你能夠假設每一個輸入只對應惟一的答案，並且你不能夠重複使用相同的元素。

示例:

輸入: numbers = [2, 7, 11, 15], target = 9
輸出: [1,2]
解釋: 2 與 7 之和等於目標數 9 。所以 index1 = 1, index2 = 2 。

---

 1 class Solution {
 2     func twoSum(_ numbers: [Int], _ target: Int) -> [Int] {
 3         var leftIndex:Int = 0
 4         var rightIndex:Int = numbers.count - 1
 5         while (leftIndex < rightIndex)
 6         {
 7             var sum = numbers[leftIndex] + numbers[rightIndex]
 8             if sum == target 
 9             {
10                 return [leftIndex + 1,rightIndex + 1]
11             }
12             else if sum < target
13             {
14                 leftIndex += 1
15             }
16             else
17             {
18                 rightIndex -= 1
19             }
20         }
21         return []
22     }
23 }

---

16ms

 1 class Solution {
 2     func twoSum(_ numbers: [Int], _ target: Int) -> [Int] {
 3         guard numbers.count >= 2 else {
 4             return []
 5         }
 6         var dic: [Int:Int] = [:]
 7         for i in 0..<numbers.count {
 8             let t = target - numbers[i]
 9             if dic.keys.contains(t) {
10                 return [dic[t]!+1, i+1]
11             }
12             dic[numbers[i]] = i
13         }
14         return []
15     }
16 }

---

24ms

 1 class Solution {
 2     func twoSum(_ numbers: [Int], _ target: Int) -> [Int] {
 3         var numIndexDict = [Int : Int]()
 4         for (index, num) in numbers.enumerated() {
 5             numIndexDict[num] = index
 6         }
 7         
 8         for (index, num) in numbers.enumerated() {
 9             if let diffIndex = numIndexDict[target - num] {
10                 return [index + 1, diffIndex + 1]
11             }
12         }
13         
14         return [Int]()
15     }
16 }