992. Subarrays with K Different Integers

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HashTable, Two Pointers, Sliding Windows

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// import java.util.*;
class Solution {
    static int subarraysWithKDistinct(int[] A, int K) {
        return atMostK(A, K) - atMostK(A, K - 1);
    }

    static int atMostK(int[] A, int K) {
        int start = 0, end = 0;
        int len = 0;
        Map<Integer, Integer> map = new HashMap<>();

        while (end < A.length) {
            int endNum = A[end];
            map.put(endNum, map.getOrDefault(endNum, 0) + 1);
            end++;
            while (map.size() > K) {
                int startNum = A[start];
                map.put(startNum, map.get(startNum) - 1);
                if (map.get(startNum) == 0) {
                    map.remove(startNum);
                }
                start++;
            }
            len += end - start;
        }
        return len;
    }
}
/*
public class MyClass {
    public static void main(String[] args) {
        int[] A = { 1, 2, 1, 2, 3 };
        int K = 2;
        System.out.println(Solution.subarraysWithKDistinct(A, K));
    }
}*/

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