Skip to content

2537. Count the Number of Good Subarrays 👍

  • Time: $O(n)$
  • Space: $O(n)$
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
class Solution {
 public:
  long long countGood(vector<int>& nums, int k) {
    long ans = 0;
    int pairs = 0;
    unordered_map<int, int> count;

    for (int l = 0, r = 0; r < nums.size(); ++r) {
      // Since there're count[r] nums[r]s, including nums[r] to the window will
      // increase the number of good subarrays by count[r].
      pairs += count[nums[r]]++;
      while (pairs >= k)
        pairs -= --count[nums[l++]];
      // nums[0..r], nums[1..r], ..., nums[l - 1..r] are good subarrays, so add
      // l to `ans`.
      ans += l;
    }

    return ans;
  }
};