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Day11_ContinuousSubarraySum.cpp
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Day11_ContinuousSubarraySum.cpp
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// Given an integer array nums and an integer k, return true if nums has a good subarray or false otherwise.
// A good subarray is a subarray where:
// its length is at least two, and
// the sum of the elements of the subarray is a multiple of k.
// Note that:
// A subarray is a contiguous part of the array.
// An integer x is a multiple of k if there exists an integer n such that x = n * k. 0 is always a multiple of k.
// Example 1:
// Input: nums = [23,2,4,6,7], k = 6
// Output: true
// Explanation: [2, 4] is a continuous subarray of size 2 whose elements sum up to 6.
// Example 2:
// Input: nums = [23,2,6,4,7], k = 6
// Output: true
// Explanation: [23, 2, 6, 4, 7] is an continuous subarray of size 5 whose elements sum up to 42.
// 42 is a multiple of 6 because 42 = 7 * 6 and 7 is an integer.
// Example 3:
// Input: nums = [23,2,6,4,7], k = 13
// Output: false
// Constraints:
// 1 <= nums.length <= 105
// 0 <= nums[i] <= 109
// 0 <= sum(nums[i]) <= 231 - 1
// 1 <= k <= 231 - 1
// Topics
// Array
// Hash Table
// Math
// Prefix Sum
// Solution:
class Solution {
public:
bool checkSubarraySum(vector<int>& nums, int k) {
unordered_map<int, int> remainderMap;
remainderMap[0] = -1;
int prefixSum = 0;
for (int i = 0; i < nums.size(); ++i) {
prefixSum += nums[i];
int remainder = prefixSum % k;
if (remainder < 0) {
remainder += k;
}
if (remainderMap.find(remainder) != remainderMap.end()) {
if (i - remainderMap[remainder] > 1) {
return true;
}
} else {
remainderMap[remainder] = i;
}
}
return false;
}
};