548.Intersection of Two Arrays II

public class Solution {
/**
 * @param nums1 an integer array
 * @param nums2 an integer array
 * @return an integer array
 */
public int[] intersection(int[] nums1, int[] nums2) {
    // Write your code here
    Map<Integer,Integer> map = new HashMap<>();
    int length1 = nums1.length;
    for (int i = 0; i < length1; i++) {
        if (map.containsKey(nums1[i])) {
            map.put(nums1[i], map.get(nums1[i]) + 1);
        } else {
            map.put(nums1[i], 1);
        }
    }
    ArrayList<Integer> list = new ArrayList<>();
    int length2 =  nums2.length;
    for (int i = 0; i < length2; i++) {
       if (map.containsKey(nums2[i])) {
           list.add(nums2[i]);
           if (map.get(nums2[i]) == 1) map.remove(nums2[i]);
           else map.put(nums2[i], map.get(nums2[i]) - 1);
       }  
    }
    int length = list.size();
    int[] result = new int[length];
    for (int i = 0; i < length; i++)  {
        result[i] = list.get(i);
    }
    return result;
}
}