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website/content/ChapterFour/0350.Intersection-of-Two-Arrays-II.md

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+# [350. Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/)
+
+## 题目
+
+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?
+
+## 题目大意
+
+这题是第 349 题的加强版。要求输出 2 个数组的交集元素，如果元素出现多次，要输出多次。
+
+## 解题思路
+
+这一题还是延续第 349 题的思路。把数组一中的数字都放进字典中，另外字典的 key 是数组中的数字，value 是这个数字出现的次数。在扫描数组二的时候，每取出一个存在的数组，把字典中的 value 减一。如果 value 是 0 代表不存在这个数字。
+
+
+
+
+
+## 代码
+
+```go
+
+package leetcode
+
+func intersect(nums1 []int, nums2 []int) []int {
+	m := map[int]int{}
+	var res []int
+	for _, n := range nums1 {
+		m[n]++
+	}
+	for _, n := range nums2 {
+		if m[n] > 0 {
+			res = append(res, n)
+			m[n]--
+		}
+	}
+	return res
+}
+
+```