LeetCode（350）Intersection of Two Arrays II

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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 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?

分析

求含重复元素的两数组交集，同样采用哈希的思想，求交集同时更新元素个数。

代码

#include <iostream>
#include <cstdlib>
#include <vector>
#include <map>

using namespace std;

class Solution {
public:
	vector<int> intersect(vector<int>& nums1, vector<int>& nums2) {
		if (nums1.empty() || nums2.empty())
			return vector<int>();

		int l1 = nums1.size(), l2 = nums2.size();
		map<int, int> m;
		for (int i = 0; i < l1; ++i)
		{
			++m[nums1[i]];
		}//for

		vector<int> ret;
		for (int i = 0; i < l2; ++i)
		{
			if (m[nums2[i]] > 0)
			{
				ret.push_back(nums2[i]);
				--m[nums2[i]];
			}//if
		}//for

		return ret;
	}
};

int main()
{
	vector<int> v1 = { 1,2,2,1 }, v2 = { 2,2 };
	vector<int> ret = Solution().intersect(v1, v2);

	system("pause");
	return 0;
}

GitHub源码