350. Intersection of Two Arrays II

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

Example 1:

Input: nums1 = [1,2,2,1], nums2 = [2,2]
Output: [2,2]

Example 2:

Input: nums1 = [4,9,5], nums2 = [9,4,9,8,4]
Output: [4,9]

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?

350. Intersection of Two Arrays II
struct Solution;

use std::collections::HashMap;
use std::collections::HashSet;

impl Solution {
    fn intersect(nums1: Vec<i32>, nums2: Vec<i32>) -> Vec<i32> {
        let mut hm1: HashMap<i32, i32> = HashMap::new();
        let hs1: HashSet<i32> = nums1.clone().into_iter().collect();
        nums1.iter().for_each(|&x| {
            *hm1.entry(x).or_default() += 1;
        });
        let mut hm2: HashMap<i32, i32> = HashMap::new();
        let hs2: HashSet<i32> = nums2.clone().into_iter().collect();
        nums2.iter().for_each(|&x| {
            *hm2.entry(x).or_default() += 1;
        });
        let bitand = &hs1 & &hs2;
        let mut res: Vec<i32> = vec![];
        bitand.iter().for_each(|&x| {
            let c1 = hm1[&x];
            let c2 = hm2[&x];
            let min = i32::min(c1, c2);
            (0..min).for_each(|_| {
                res.push(x);
            });
        });
        res
    }
}

#[test]
fn test() {
    let nums1 = vec![1, 2, 2, 1];
    let nums2 = vec![2, 2];
    assert_eq!(Solution::intersect(nums1, nums2), vec![2, 2]);
}