350. Intersection of Two Arrays II

import java.util.ArrayList;
import java.util.HashMap;

/**
 * Created by Joe on 2018/3/18.
 * 350. Intersection of Two Arrays II
 * https://leetcode.com/problems/intersection-of-two-arrays-ii/description/
 */
public class P350 {
    public int[] intersect(int[] nums1, int[] nums2) {
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        ArrayList<Integer> result = new ArrayList<Integer>();
        for(int i = 0; i < nums1.length; i++)
        {
            if(map.containsKey(nums1[i])) map.put(nums1[i], map.get(nums1[i])+1);
            else map.put(nums1[i], 1);
        }

        for(int i = 0; i < nums2.length; i++)
        {
            if(map.containsKey(nums2[i]) && map.get(nums2[i]) > 0)
            {
                result.add(nums2[i]);
                map.put(nums2[i], map.get(nums2[i])-1);
            }
        }

        int[] r = new int[result.size()];
        for(int i = 0; i < result.size(); i++)
        {
            r[i] = result.get(i);
        }

        //爲什麼不用 toArray() 方法？ 因爲返回對象是個 T[] 泛型
        //只能返回 Integer[] 而不能 int[] 
        return r;
    }
}