// Runtime: 2 ms, faster than 99.90% of Java online submissions for Continuous Subarray Sum.
// Memory Usage: 39.9 MB, less than 88.24% of Java online submissions for Continuous Subarray Sum.
class Solution {
    public boolean checkSubarraySum(int[] nums, int k) {
        int len = nums.length;
        if (len == 0) return false;

        int cs = 0;
        Map<Integer, Integer> occ = new HashMap<Integer, Integer>();
        occ.put(0, -1);

        for (int i = 0; i < len; i++) {
            cs += nums[i];

            if (cs >= k && k != 0) cs %= k;

            Integer prev = occ.get(cs);
            if (prev == null) occ.put(cs, i);
            else if (i - prev > 1) return true;
        }

        return false;
    }
}