Continuous Subarray Sum

Given a list of non-negative numbers and a target integer k, write a function to check if the array has a continuous subarray of size at least 2 that sums up to a multiple of k, that is, sums up to n*k where n is also an integer.

 

Example 1:

Input: [23, 2, 4, 6, 7],  k=6
Output: True
Explanation: Because [2, 4] is a continuous subarray of size 2 and sums up to 6.

Example 2:

Input: [23, 2, 6, 4, 7],  k=6
Output: True
Explanation: Because [23, 2, 6, 4, 7] is an continuous subarray of size 5 and sums up to 42.

 

Constraints:


Solution:

class Solution {
    public boolean checkSubarraySum(int[] nums, int k) {
        if (nums.length <= 1) return false; 
        for (int i = 1; i < nums.length; i ++) {
            if (nums[i] == 0 && nums[i - 1] == 0) {
                return true;
            }
        }
        if (k == 0) return false;
        k = Math.abs(k);
        if (k == 1) return true;
        Map<Integer, Integer> map = new HashMap();
        int sum = nums[0];
        map.put(0, -1);
        map.put(sum, 0);
        for (int i = 1; i < nums.length; i ++) {
            sum += nums[i];
            for (int j = 1; j * k <= sum; j ++) {
                // sum - target = j * k
                int target = sum - j * k;
                if (map.containsKey(target) && (i - map.get(target)) > 1) {
                    return true;
                }
            }
            map.putIfAbsent(sum, i);
        }
        return false;
    }
}