Java找出不重复无序数组中和为n的两数的下标

 1 import java.util.HashMap;
 2 import java.util.Iterator;
 3 import java.util.Map;
 4 
 5 public class Demo5 {
 6 
 7     public static void main(String[] args) {
 8 
 9         int[] arr = new int[]{3, 4, 5, 9, 8};
10         int num = 8;
11         int[] ret = getIndex(arr, num);
12         System.out.println("index of two number:" + ret[0]+" " + ret[1]);
13 
14     }
15 
16     //找到这两个数的下标，并以长度为2的数组形式返回
17     public static int[] getIndex(int[] arr, int num){
18         
19         int[] ret = new int[2];   //长度为2的数组
20         HashMap<Integer, Integer> hashMap = new HashMap<>();
21         int index = 0;
22         
23         //将每个数字及其下标放入map中
24         for (int i : arr) {
25             hashMap.put(i, index++ );
26         }
27 
28         //遍历 HashMap 并判断
29         Iterator iterator = hashMap.entrySet().iterator();
30         while (iterator.hasNext()){
31             Map.Entry entry = (Map.Entry)iterator.next();
32 
33             int value = (int) entry.getKey();
34             int subValue = num - value;
35 
36             if (hashMap.containsKey(subValue)){
37                 //找到了
38                 ret[0] = (int) entry.getValue();
39                 ret[1] = hashMap.get(subValue);
40                 break;
41             }
42         }
43         return ret;
44 
45     }
46 }