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

 1 package TwoSets;
 2 import java.util.*;
 3 
 4 public class Solution {
 5     public ArrayList<Integer> findDiff(int[] arr1, int[] arr2) {
 6         ArrayList<Integer> res = new ArrayList<Integer>();
 7         HashMap<Integer, Integer> m1 = new HashMap<Integer, Integer>();
 8         for (int item1 : arr1) {
 9             if (!m1.containsKey(item1)) {
10                 m1.put(item1, 1);
11             }
12             else {
13                 m1.put(item1, m1.get(item1)+1);
14             }
15         }
16         for (int item2 : arr2) {
17             if (m1.containsKey(item2)) {
18                 m1.put(item2, m1.get(item2)-1);
19             }
20             if (m1.get(item2) == 0) m1.remove(item2);
21         }
22         for (int elem : m1.keySet()) {
23             int num = m1.get(elem);
24             while (num > 0) {
25                 res.add(elem);
26                 num--;
27             }
28         }
29         return res;
30     }
31     
32 
33     /**
34      * @param args
35      */
36     public static void main(String[] args) {
37         // TODO Auto-generated method stub
38         Solution sol = new Solution();
39         ArrayList<Integer> res = sol.findDiff(new int[]{1,2,3,4,4,5}, new int[]{2,4});
40         System.out.println(res);
41     }
42 
43 }