560. Subarray Sum Equals K

记录前面的sum https://leetcode.com/problems/subarray-sum-equals-k/discuss/102106/Java-Solution-PreSum-+-HashMap

 

 

 1 class Solution {
 2     public int subarraySum(int[] nums, int k) {
 3         if(nums.length == 0) return 0;
 4         int count = 0;
 5         for(int i = 0; i < nums.length; i++){
 6             if(nums[i] == k){
 7                 count++;
 8             }
 9             int j = i+1;
10             int sum = nums[i];
11             while(j < nums.length){
12                 sum += nums[j]; 
13                 if(sum == k){
14                     count++;
15                     j++;
16                 }else{
17                     j++;
18                 }
19             }
20             
21         }
22         return count;
23     }
24 }
25 
26 
27 //New
28 class Solution {
29     public int subarraySum(int[] nums, int k) {
30         if(nums.length == 0) return 0;
31         Map<Integer, Integer> map = new HashMap<>();
32         int res = 0;
33         int sum = 0;
34         map.put(0, 1);
35         for(int i = 0; i < nums.length; i++){
36             sum += nums[i];
37             if(map.containsKey(sum - k)){
38                 res += map.get(sum - k);
39             }
40             map.put(sum, map.getOrDefault(sum, 0) + 1);
41         }
42         return res;
43     }
44 }

 

posted @ 2018-10-22 03:04  jasoncool1  阅读(118)  评论(0)  编辑  收藏  举报