LeetCode #560 - Subarray Sum Equals K

题目描述：

Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.

Example 1:

Input:nums = [1,1,1], k = 2
Output: 2

Note:

1. The length of the array is in range [1, 20,000].
2. The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].

找到数组中的所有子数组，满足子数组之和等于目标值k。先计算[0,i]区间的数组累积和，那么对于当前的累计和sum，如果之前有x个累计和等于sum-k，那么就能找到x个子数组之和等于k，所以在每次计算累积和时，还要用哈希表存储累积和对应的次数。

class Solution {
public:
    int subarraySum(vector& nums, int k) {
        int sum=0;
        unordered_map hash;
        hash[0]=1;
        int count=0;
        for(int i=0;i