349. Intersection of Two Arrays*

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

Example:
Given nums1 = [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.

Method I:

   Use the dictionary in python to store values from nums1. Loop in nums2 to find the intersection of nums1 and nums2

class Solution(object):
    def intersection(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        dictionary = {}
        intersection_set = []
        for num1 in nums1:
            if num1 in dictionary:
                dictionary[num1] += 1
            else:
                dictionary [num1] = 1
        for num2 in nums2:
            if num2 in dictionary and (num2  not in intersection_set):
                intersection_set.append(num2)
        return intersection_set  

Method II:

Use set in python

def intersection1(self, nums1,nums2):  
return list(set(nums1)& set(nums2))

Method III:

Sort two lists respectively, and use pointers to  find intersection

    def intersection2(self, nums1, nums2):
        pointer1 = 0
        pointer2 = 0
        nums1.sort()
        nums2.sort()
        intersection_set=[]
        while pointer1<len(nums1) and pointer2<len(nums2):
             if nums1[pointer1]<nums2[pointer2]:
                 pointer1 +=1
             elif nums1[pointer1]>nums2[pointer2]:
                 pointer2 +=1
             elif nums1[pointer1] not in intersection_set:
                 intersection_set.append(nums1[pointer1])
                 pointer1 +=1
                 pointer2 +=1
             else:
                 pointer1 +=1
                 pointer2 +=1               
                 
        return intersection_set

Reference :http://blog.youkuaiyun.com/coder_orz/article/details/51452615