[Swift]LeetCode350. 兩個數組的交集 II | Intersection of Two Arrays II

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➤微信公衆號：山青詠芝（shanqingyongzhi）
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Given two arrays, write a function to compute their intersection.

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2] Output: [2,2] 

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4] Output: [4,9]

Note:

• Each element in the result should appear as many times as it shows in both arrays.
• The result can be in any order.

Follow up:

• What if the given array is already sorted? How would you optimize your algorithm?
• What if nums1's size is small compared to nums2's size? Which algorithm is better?
• What if elements of nums2 are stored on disk, and the memory is limited such that you cannot load all elements into the memory at once?

---

 1 class Solution {
 2     func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
 3         //定義兩個指針
 4         var cur1:Int = 0
 5         var cur2:Int = 0
 6         var res:[Int] = [Int]()       
 7         var arr1: Array<Int> = nums1
 8         var arr2: Array<Int> = nums2
 9         //排序
10         arr1.sort(){$0 < $1}
11         arr2.sort(){$0 < $1}
12         while(cur1 <  arr1.count && cur2 < arr2.count)
13         {
14             var num1 = arr1[cur1]
15             var num2 = arr2[cur2]
16             if num1 == num2
17             {
18                 res.append(num1)
19                 cur1 += 1
20                 cur2 += 1
21             }
22             else if num1 < num2
23             {
24                 cur1 += 1
25             }
26             else
27             {
28                  cur2 += 1
29             }
30         }
31         return res
32     }
33 }

---

12ms

 1 class Solution {
 2     func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
 3         var frequency = Dictionary( nums1.map{ ($0, 1) }, uniquingKeysWith: +)
 4         var results = [Int]()
 5         for num in nums2 {
 6             if let value = frequency[num], value > 0 {
 7                 frequency[num] = value - 1
 8                 results.append(num)
 9             }
10         }
11         return results
12     }
13 }

---

16ms

 1 class Solution {
 2     func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
 3         var map: [Int: Int] = [:]
 4         for num in nums1 {
 5             if let count = map[num] {
 6                 map[num] = count + 1
 7             } else {
 8                 map[num] = 1
 9             }
10         }
11 
12         var result: [Int] = []
13         for num in nums2 {
14             if let count = map[num], count >= 1 {
15                 result.append(num)
16                 map[num] = count - 1
17             }
18         }
19         return result
20     }
21 }

---

20ms

 1 class Solution {
 2     func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
 3     var nums1 = nums1.sorted(by: <)
 4     var nums2 = nums2.sorted(by: <)
 5     
 6     var i:Int = 0, j:Int = 0
 7     
 8     var n1:Int = 0, n2:Int = 0
 9     
10     var results:[Int] = Array()
11     
12     while i < nums1.count && j < nums2.count {
13         n1 = nums1[i]
14         n2 = nums2[j]
15         if n1 < n2 {
16             i += 1
17         }else if n1 > n2 {
18             j += 1
19         }else {
20             results.append(n1)
21             i += 1
22             j += 1
23         }
24     }
25     return results
26     }
27 }

---

20ms

 1 class Solution {
 2 
 3     func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
 4         var dic = [Int: Int]()
 5         var result = [Int]()
 6         for value in nums1{
 7             if dic[value] != nil {
 8                 dic[value]! += 1
 9             }else{
10                 dic[value] = 1
11             }
12         }
13         for value in nums2 {
14             if dic[value] != nil && dic[value] != 0{
15                 result.append(value)
16                 dic[value]! -= 1
17             }
18         }
19         return result
20     }
21 }