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:
- 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.
Special case:
nums = [0,0], k = 0, return = True
Solution: Prefix Sum Reminder
Time complexity: O(n)
Space complexity: O(min(n, k))
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
// Author: Huahua // Running time: 16 ms (<99.62%) class Solution { public: bool checkSubarraySum(vector<int>& nums, int k) { unordered_map<int, int> m; // sum % k -> first index m[0] = -1; int sum = 0; for (int i = 0; i < nums.size(); ++i) { sum += nums[i]; if (k != 0) sum %= k; if (m.count(sum)) { if (i - m.at(sum) > 1) return true; } else { m[sum] = i; } } return false; } }; |