Continuous Subarray Sum

Problem:

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 the 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.

Note:

1. The length of the array won't exceed 10,000.
2. You may assume the sum of all the numbers is in the range of a signed 32-bit integer.

Analysis:

这道踢的通用价值非常低。面试的时候根本想不出来判断条件。

Solution:

Note 0 can not be %. 

class Solution {
    public boolean checkSubarraySum(int[] nums, int k) {
        Map<Integer, Integer> map = new HashMap<>();
        int sum = 0;
        map.put(0, -1);
        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            int rem = (k == 0) ? sum : sum % k;
            if (map.containsKey(rem)) {
                if (i - map.get(rem) > 1)
                    return true;
            } else {
                map.put(rem, i);
            }
        }
        return false;
    }
}