[Swift]LeetCode350. 两个数组的交集 II | Intersection of Two Arrays II

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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?

---

class Solution {
    func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
        //定义两个指针
        var cur1:Int = 0
        var cur2:Int = 0
        var res:[Int] = [Int]()       
        var arr1: Array<Int> = nums1
        var arr2: Array<Int> = nums2
        //排序
        arr1.sort(){$0 < $1}
        arr2.sort(){$0 < $1}
        while(cur1 <  arr1.count && cur2 < arr2.count)
        {
            var num1 = arr1[cur1]
            var num2 = arr2[cur2]
            if num1 == num2
            {
                res.append(num1)
                cur1 += 1
                cur2 += 1
            }
            else if num1 < num2
            {
                cur1 += 1
            }
            else
            {
                 cur2 += 1
            }
        }
        return res
    }
}

---

12ms

class Solution {
    func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
        var frequency = Dictionary( nums1.map{ ($0, 1) }, uniquingKeysWith: +)
        var results = [Int]()
        for num in nums2 {
            if let value = frequency[num], value > 0 {
                frequency[num] = value - 1
                results.append(num)
            }
        }
        return results
    }
}

---

16ms

class Solution {
    func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
        var map: [Int: Int] = [:]
        for num in nums1 {
            if let count = map[num] {
                map[num] = count + 1
            } else {
                map[num] = 1
            }
        }

        var result: [Int] = []
        for num in nums2 {
            if let count = map[num], count >= 1 {
                result.append(num)
                map[num] = count - 1
            }
        }
        return result
    }
}

---

20ms

class Solution {
    func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
    var nums1 = nums1.sorted(by: <)
    var nums2 = nums2.sorted(by: <)
    
    var i:Int = 0, j:Int = 0
    
    var n1:Int = 0, n2:Int = 0
    
    var results:[Int] = Array()
    
    while i < nums1.count && j < nums2.count {
        n1 = nums1[i]
        n2 = nums2[j]
        if n1 < n2 {
            i += 1
        }else if n1 > n2 {
            j += 1
        }else {
            results.append(n1)
            i += 1
            j += 1
        }
    }
    return results
    }
}

---

20ms

class Solution {

    func intersect(_ nums1: [Int], _ nums2: [Int]) -> [Int] {
        var dic = [Int: Int]()
        var result = [Int]()
        for value in nums1{
            if dic[value] != nil {
                dic[value]! += 1
            }else{
                dic[value] = 1
            }
        }
        for value in nums2 {
            if dic[value] != nil && dic[value] != 0{
                result.append(value)
                dic[value]! -= 1
            }
        }
        return result
    }
}