leetcode-560 和为K的子数组 Java

https://leetcode-cn.com/problems/subarray-sum-equals-k/solution/he-wei-kde-zi-shu-zu-by-leetcode-solution/

方法一：

class Solution {
    public int subarraySum(int[] nums, int k) {
        int count = 0, pre = 0;
        HashMap <Integer, Integer> mp = new HashMap<>();
        mp.put(0, 1);
        for (int i = 0; i < nums.length; i++) {
            pre += nums[i];
            if (mp.containsKey(pre - k))
                count += mp.get(pre - k);
            mp.put(pre, mp.getOrDefault(pre, 0) + 1);
        }
        return count;
    }
}

方法二：

class Solution {
    public int subarraySum(int[] nums, int k) {
        int count = 0;
        for (int start = 0; start < nums.length; ++start) {
            int sum = 0;
            for (int end = start; end >= 0; --end) {
                sum += nums[end];
                if (sum == k) {
                    count++;
                }
            }
        }
        return count;
    }
}