leetcode 992 - Subarrays with K Different Integers

https://leetcode.com/problems/subarrays-with-k-different-integers/
https://leetcode.com/problems/subarrays-with-k-different-integers/discuss/523136/JavaC%2B%2BPython-Sliding-Window

Given an array A of positive integers, call a (contiguous, not necessarily distinct) subarray of A good if the number of different integers in that subarray is exactly K.

(For example, [1,2,3,1,2] has 3 different integers: 1, 2, and 3.)

Return the number of good subarrays of A.

Example 1:

Input: A = [1,2,1,2,3], K = 2
Output: 7
Explanation: Subarrays formed with exactly 2 different integers: [1,2], [2,1], [1,2], [2,3], [1,2,1], [2,1,2], [1,2,1,2].
Example 2:

Input: A = [1,2,1,3,4], K = 3
Output: 3
Explanation: Subarrays formed with exactly 3 different integers: [1,2,1,3], [2,1,3], [1,3,4].

Note:

1 <= A.length <= 20000
1 <= A[i] <= A.length
1 <= K <= A.length

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class Solution {
public:
int subarraysWithKDistinct(vector<int>& A, int K) {
return atMostK(A, K) - atMostK(A, K - 1);
}

int atMostK(vector<int>& A, int K) {
int size = A.size();
unordered_map<int, int> count;

int total = 0;
int i = 0;

for (int j = 0; j < size; j++) {
count[A[j]]++;

while (count.size() > K) {
int key = A[i++];
if (--count[key] == 0)
count.erase(key);
}

total += j - i + 1;
}

return total;
}
};