[leetcode] 350. Intersection of Two Arrays II 解题报告

题目链接: https://leetcode.com/problems/intersection-of-two-arrays-ii/
Given two arrays, write a function to compute their intersection.

Example:

Given nums1 =

[1, 2, 2, 1]

, nums2 =

[2,
2]

, return

[2, 2]

.

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 num2'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?

思路: 还是用hash表, 简单粗暴, 如果是有序的可以不用hash表, 同时扫描两个数组, 找相同的. 如果nums2在磁盘中, 用hash表无影响

代码如下:

class Solution {
public:
vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
if(nums1.size()==0 || nums2.size()==0) return vector<int>();
vector<int> result;
unordered_map<int, int> hash;
for(auto val: nums1) hash[val]++;
for(auto val: nums2)
{
if(hash.count(val) && hash[val]>0) result.push_back(val);
hash[val]--;
}
return result;
}
};