Lintcode: Subarray Sum 解题报告

 1 public class Solution {
 2     /**
 3      * @param nums: A list of integers
 4      * @return: A list of integers includes the index of the first number 
 5      *          and the index of the last number
 6      */
 7     public ArrayList<Integer> subarraySum(int[] nums) {
 8         // write your code here
 9         
10         int len = nums.length;
11         
12         ArrayList<Integer> ret = new ArrayList<Integer>();
13         
14         HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
15         
16         // We set the index -1 sum to be 0 to let us more convient to count.
17         map.put(0, -1);
18         
19         int sum = 0;
20         for (int i = 0; i < len; i++) {
21             sum += nums[i];
22             
23             if (map.containsKey(sum)) {
24                 // For example: 
25                 //        -3  1  2 -3 4
26                 // SUM: 0 -3 -2  0 -3 1
27                 // then we got the solution is : 0 - 2
28                 ret.add(map.get(sum) + 1);
29                 ret.add(i);
30                 return ret;
31             }
32             
33             // Store the key:value of sum:index.
34             map.put(sum, i);
35         }
36         
37         return ret;
38     }
39 }