LeetCode:和为K的子数组

class Solution {
    public int subarraySum(int[] nums, int k) {
        Map<Integer,Integer> preSumMap = new HashMap<>();

        preSumMap.put(0,1);
        //记录一共多少子数组
        int count = 0;
        //记录当前总和
        int preSum = 0;

        for(int i = 0; i < nums.length; i++){
            preSum += nums[i];
            //目标总和 = 之前总和 - k
            int target = preSum - k;

            if(preSumMap.containsKey(target)){
                count += preSumMap.get(target);
            }
            //将当前总和放到PreSumMap中，便于后续查找
            preSumMap.put(preSum,preSumMap.getOrDefault(preSum,0) + 1);
        } 
        return count;
    }
}

preSumMap.put(preSum,preSumMap.getOrDefault(preSum,0) + 1):

查找preSumMap中是否有preSum这个数字，有把次数返回，没有就是0