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Formatted question description: https://leetcode.ca/all/1852.html

1852. Distinct Numbers in Each Subarray

Level

Medium

Description

Given an integer array nums and an integer k, you are asked to construct the array ans of size n-k+1 where ans[i] is the number of distinct numbers in the subarray nums[i:i+k-1] = [nums[i], nums[i+1], ..., nums[i+k-1]].

Return the array ans.

Example 1:

Input: nums = [1,2,3,2,2,1,3], k = 3

Output: [3,2,2,2,3]

Explanation: The number of distinct elements in each subarray goes as follows:

• nums[0:2] = [1,2,3] so ans[0] = 3
• nums[1:3] = [2,3,2] so ans[1] = 2
• nums[2:4] = [3,2,2] so ans[2] = 2
• nums[3:5] = [2,2,1] so ans[3] = 2
• nums[4:6] = [2,1,3] so ans[4] = 3

Example 2:

Input: nums = [1,1,1,1,2,3,4], k = 4

Output: [1,2,3,4]

Explanation: The number of distinct elements in each subarray goes as follows:

• nums[0:3] = [1,1,1,1] so ans[0] = 1
• nums[1:4] = [1,1,1,2] so ans[1] = 2
• nums[2:5] = [1,1,2,3] so ans[2] = 3
• nums[3:6] = [1,2,3,4] so ans[3] = 4

Constraints:

• 1 <= k <= nums.length <= 10^5
• 1 <= nums[i] <= 10^5

Solution

Use a hash map to store each number’s occurrences in the sliding window. For each i from k - 1 to n - 1, the corresponding value in ans is the size of the map.

• Java
• C++
• Python
• Go

• class Solution {
      public int[] distinctNumbers(int[] nums, int k) {
          int n = nums.length;
          int[] ans = new int[n - k + 1];
          Map<Integer, Integer> map = new HashMap<Integer, Integer>();
          for (int i = 0; i < k; i++) {
              int num = nums[i];
              map.put(num, map.getOrDefault(num, 0) + 1);
          }
          ans[0] = map.size();
          for (int i = k; i < n; i++) {
              int prev = nums[i - k], curr = nums[i];
              map.put(prev, map.get(prev) - 1);
              if (map.get(prev) == 0)
                  map.remove(prev);
              map.put(curr, map.getOrDefault(curr, 0) + 1);
              ans[i - k + 1] = map.size();
          }
          return ans;
      }
  }
  
  ############
  
  class Solution {
      public int[] distinctNumbers(int[] nums, int k) {
          int[] cnt = new int[100010];
          int x = 0;
          for (int i = 0; i < k; ++i) {
              if (cnt[nums[i]]++ == 0) {
                  ++x;
              }
          }
          int n = nums.length;
          int[] ans = new int[n - k + 1];
          ans[0] = x;
          for (int i = k; i < n; ++i) {
              if (--cnt[nums[i - k]] == 0) {
                  --x;
              }
              if (cnt[nums[i]]++ == 0) {
                  ++x;
              }
              ans[i - k + 1] = x;
          }
          return ans;
      }
  }
  

• // OJ: https://leetcode.com/problems/distinct-numbers-in-each-subarray/
  // Time: O(N)
  // Space: O(N)
  class Solution {
  public:
      vector<int> distinctNumbers(vector<int>& A, int k) {
          unordered_map<int, int> cnt;
          vector<int> ans(A.size() - k + 1);
          for (int i = 0, N = A.size(); i < N; ++i) {
              cnt[A[i]]++;
              if (i - k >= 0 && --cnt[A[i - k]] == 0) cnt.erase(A[i - k]);
              if (i >= k - 1) ans[i - k + 1] = cnt.size();
          }
          return ans;
      }
  };
  

• class Solution:
      def distinctNumbers(self, nums: List[int], k: int) -> List[int]:
          n = len(nums)
          cnt = Counter(nums[:k])
          ans = [len(cnt)]
          for i in range(k, n):
              u = nums[i - k]
              cnt[u] -= 1
              if cnt[u] == 0:
                  cnt.pop(u)
  
              cnt[nums[i]] += 1
              ans.append(len(cnt))
          return ans
  
  
  

• func distinctNumbers(nums []int, k int) []int {
  	cnt := map[int]int{}
  	for _, v := range nums[:k] {
  		cnt[v]++
  	}
  	ans := []int{len(cnt)}
  	for i := k; i < len(nums); i++ {
  		u := nums[i-k]
  		cnt[u]--
  		if cnt[u] == 0 {
  			delete(cnt, u)
  		}
  		cnt[nums[i]]++
  		ans = append(ans, len(cnt))
  	}
  	return ans
  }
  

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