LC 992. Subarrays with K Different Integers

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

Runtime: 128 ms, faster than 100.00% of C++ online submissions for Subarrays with K Different Integers.

Memory Usage: 25 MB, less than 100.00% of C++ online submissions for Subarrays with K Different Integers.

class Solution {

public:

  int subarraysWithKDistinct(vector<int>& A, int K) {

    return atMostK(A, K) - atMostK(A,K-);

  }

  int atMostK(vector<int>& A, int K) {

    int i = ,res = ;

    unordered_map<int,int> mp;

    for(int j=; j<A.size(); j++) {

      if(!mp[A[j]]++) K--;

      while(K<){

        if(!--mp[A[i]]) K++;

        i++;

      }

      res += j - i + ;

    }

    return res;

  }

};

巴特西

LC 992. Subarrays with K Different Integers

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