Intersection of Two Arrays II-LeetCode

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?

Java Solution :

class Solution {
 public int[] intersect(int[] nums1, int[] nums2) {
  HashMap<Integer,Integer> map = new HashMap<Integer,Integer>();

  for(int i : nums1){
   if(!map.containsKey(i)){
    map.put(i,1); 
   }else{
    map.put(i,map.get(i)+1);
   }
  }
  ArrayList<Integer> list = new ArrayList<Integer>();

  for(int j : nums2){
   if(map.containsKey(j)){
    if(map.get(j)>=1){
     list.add(j);
     map.put(j,(map.get(j))-1);

    }
   }
  }

  int[] common = new int[list.size()];
  int j =0;

  for(int k:list){
   common[j]=k;
   j++;

  }
  return common;
 }
}