LeetCode [992] Subarrays with K Different Integers

 992. Subarrays with K Different Integers

Hard

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. 1 <= A.length <= 20000
2. 1 <= A[i] <= A.length
3. 1 <= K <= A.length

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class Solution { public int subarraysWithKDistinct(int[] A, int K) { return atMost(A, K)-atMost(A, K-1); } int atMost(int[] A, int K){ int n = A.length; int i = 0, j = 0, cnt = 0; int ret = 0; Map<Integer, Integer> map = new HashMap<>(); while(j<n){ int key = A[j++]; if(map.getOrDefault(key, 0)==0){ cnt++; } map.put(key, map.getOrDefault(key, 0)+1); while(cnt>K){ int last = A[i++]; map.put(last, map.get(last)-1); if(map.get(last)==0) cnt--; } ret += j-i+1; } return ret; } }