G面经prepare: set difference

给你A{1,2,3,4,4,5}， B{2,4}，求A-B={1,3,4,5},很简单. visit 1

只用一个HashMap

 package TwoSets;
 import java.util.*;
 
 public class Solution {
     public ArrayList<Integer> findDiff(int[] arr1, int[] arr2) {
         ArrayList<Integer> res = new ArrayList<Integer>();
         HashMap<Integer, Integer> m1 = new HashMap<Integer, Integer>();
         for (int item1 : arr1) {
             if (!m1.containsKey(item1)) {
                 m1.put(item1, 1);
             }
             else {
                 m1.put(item1, m1.get(item1)+1);
             }
         }
         for (int item2 : arr2) {
             if (m1.containsKey(item2)) {
                 m1.put(item2, m1.get(item2)-1);
             }
             if (m1.get(item2) == 0) m1.remove(item2);
         }
         for (int elem : m1.keySet()) {
             int num = m1.get(elem);
             while (num > 0) {
                 res.add(elem);
                 num--;
             }
         }
         return res;
     }
 
     /**
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         Solution sol = new Solution();
         ArrayList<Integer> res = sol.findDiff(new int[]{1,2,3,4,4,5}, new int[]{2,4});
         System.out.println(res);
     }
 
 }