Leetcode题目:Intersection of Two Arrays II
题目:
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?
题目解答:和上一题一样,这次不需要去重复。
代码如下:
class Solution { public: vector<int> intersect(vector<int>& nums1, vector<int>& nums2) { sort(nums1.begin(), nums1.end()); //vector<int>::iterator end_unique = unique(nums1.begin(), nums1.end()); // nums1.erase(end_unique, nums1.end()); sort(nums2.begin(),nums2.end()); // end_unique = unique(nums2.begin(), nums2.end()); //nums2.erase(end_unique, nums2.end()); vector<int>::iterator nit1 = nums1.begin(); vector<int>::iterator nit2 = nums2.begin(); vector<int> res; while((nit1 != nums1.end()) && (nit2 != nums2.end()) ) { if(*nit1 == *nit2) { res.push_back(*nit1); nit1++; nit2++; } else if(*nit1 < *nit2) { nit1++; } else { nit2++; } } return res; } };
考虑到Followup中提到的,对nums2进行排序不太好,使用哈希来编码实现,代码如下:
class Solution { public: vector<int> intersect(vector<int>& nums1, vector<int>& nums2) { unordered_map<int, int> num_map; vector<int> res; for(auto nit = nums1.begin(); nit != nums1.end(); nit++) { num_map[*nit] += 1; } for(auto nit = nums2.begin(); nit != nums2.end(); nit++) { if(num_map[*nit] >= 1) { num_map[*nit] -= 1; res.push_back(*nit); } } return res; } };