# C#LeetCode刷题之#350-两个数组的交集 II（Intersection of Two Arrays II）

Given two arrays, write a function to compute their intersection.

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

Output: [2,2]

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.

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?

```public class Program {

public static void Main(string[] args) {
var nums1 = new int[] { 4, 9, 4, 5 };
var nums2 = new int[] { 9, 4, 9, 8, 4 };

var res = Intersection(nums1, nums2);
ShowArray(res);

}

private static void ShowArray(int[] array) {
foreach(var num in array) {
Console.Write(\$"{num} ");
}
Console.WriteLine();
}

private static int[] Intersection(int[] nums1, int[] nums2) {
var list = new List<int>();
var dic = new Dictionary<int, int>();

for(var i = 0; i < nums1.Length; i++) {
if(dic.ContainsKey(nums1[i])) {
dic[nums1[i]]++;
} else {
dic[nums1[i]] = 1;
}
}

for(var i = 0; i < nums2.Length; i++) {
if(dic.ContainsKey(nums2[i]) && dic[nums2[i]] != 0) {
dic[nums2[i]]--;
}
}

return list.ToArray();
}

}```

`9 4 4`

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