> For the complete documentation index, see [llms.txt](https://rachel2011.gitbook.io/leetcode_cc150/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://rachel2011.gitbook.io/leetcode_cc150/array-and-string/intersection-of-two-arrays.md).

# Intersection of Two Arrays

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

**Example:**\
Givennums1=`[1, 2, 2, 1]`,nums2=`[2, 2]`, return`[2]`.

**Note:**

* Each element in the result must be unique.
* The result can be in any order.

```
class Solution(object):
    def intersection(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        return list(set(nums1) & set(nums2))
```

```
#use dict/hashmap to record all nums appeared in the first list, and then check if there are nums in the second list have appeared in the map.
class Solution(object):
    def intersection(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        hashmap = {}
        result = []
        for i in range(len(nums1)):
            hashmap[nums1[i]] = i
        for num2 in nums2:
            if num2 in hashmap and num2 not in result:
                result.append(num2)
        return result
```

两个指针来做，先给两个数组排序，然后用两个指针分别指向两个数组的开头，然后比较两个数组的大小，把小的数字的指针向后移，如果两个指针指的数字相等，那么看结果res是否为空，如果为空或者是最后一个数字和当前数字不等的话，将该数字加入结果res中

```
class Solution(object):
def intersection(self, nums1, nums2):
    """
    :type nums1: List[int]
    :type nums2: List[int]
    :rtype: List[int]
    """
    res = []
    nums1.sort()
    nums2.sort()
    i = j = 0
    while (i < len(nums1) and j < len(nums2)):
        if nums1[i] > nums2[j]:
            j += 1
        elif nums1[i] < nums2[j]:
            i += 1
        else:
            if not (len(res) and nums1[i] == res[len(res)-1]):
                res.append(nums1[i])
            i += 1
            j += 1

    return res
```

## 二刷：

```
class Solution(object):
    def intersection(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        result =[]
        hashmap = collections.Counter(nums1)
        for num in nums2:
            if num in hashmap and hashmap[num] > 0:
                result.append(num)
                hashmap[num] = -1
        return result
```

```
class Solution(object):
    def intersection(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        result = []
        hash=collections.Counter(nums1)
        for num2 in nums2:
            if num2 in hash and num2 not in result:
                result.append(num2)
        return result
```