523. 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.

Note:

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

Solution

DP(比较奇怪)

Corner Case:
k == 0, 0不能做除数

Pending:
HashMap算法

Complexity

O(N2) O(N)

Code

class Solution {
    public boolean checkSubarraySum(int[] nums, int k) {
        if(nums == null || nums.length == 0)
            return false;
        
        int[] dp = new int[nums.length];
        dp[0] = nums[0];
        for(int i = 1; i < nums.length; i++){
            dp[i] = dp[i-1] + nums[i];
        }
        
        for(int i = 0; i < nums.length; i++){
            for(int j = i+1; j<nums.length; j++){
                int diff = i - 1 >= 0 ? dp[j] - dp[i-1] : dp[j];
                if(k == 0){
                    if(diff == 0)
                        return true;
                }else {
                    if (diff % k == 0)
                        return true;
                }
            }
        }
        return false;
    }
}