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2080. Range Frequency Queries

Description

Design a data structure to find the frequency of a given value in a given subarray.

The frequency of a value in a subarray is the number of occurrences of that value in the subarray.

Implement the RangeFreqQuery class:

• RangeFreqQuery(int[] arr) Constructs an instance of the class with the given 0-indexed integer array arr.
• int query(int left, int right, int value) Returns the frequency of value in the subarray arr[left...right].

A subarray is a contiguous sequence of elements within an array. arr[left...right] denotes the subarray that contains the elements of nums between indices left and right (inclusive).

 

Example 1:

Input
["RangeFreqQuery", "query", "query"]
[[[12, 33, 4, 56, 22, 2, 34, 33, 22, 12, 34, 56]], [1, 2, 4], [0, 11, 33]]
Output
[null, 1, 2]

Explanation
RangeFreqQuery rangeFreqQuery = new RangeFreqQuery([12, 33, 4, 56, 22, 2, 34, 33, 22, 12, 34, 56]);
rangeFreqQuery.query(1, 2, 4); // return 1. The value 4 occurs 1 time in the subarray [33, 4]
rangeFreqQuery.query(0, 11, 33); // return 2. The value 33 occurs 2 times in the whole array.

 

Constraints:

• 1 <= arr.length <= 105
• 1 <= arr[i], value <= 104
• 0 <= left <= right < arr.length
• At most 105 calls will be made to query

Solutions

• Java
• C++
• Python
• Go

• class RangeFreqQuery {
      private Map<Integer, List<Integer>> mp = new HashMap<>();
  
      public RangeFreqQuery(int[] arr) {
          for (int i = 0; i < arr.length; ++i) {
              mp.computeIfAbsent(arr[i], k -> new ArrayList<>()).add(i);
          }
      }
  
      public int query(int left, int right, int value) {
          if (!mp.containsKey(value)) {
              return 0;
          }
          List<Integer> arr = mp.get(value);
          int l = search(arr, left - 1);
          int r = search(arr, right);
          return r - l;
      }
  
      private int search(List<Integer> arr, int val) {
          int left = 0, right = arr.size();
          while (left < right) {
              int mid = (left + right) >> 1;
              if (arr.get(mid) > val) {
                  right = mid;
              } else {
                  left = mid + 1;
              }
          }
          return left;
      }
  }
  
  /**
   * Your RangeFreqQuery object will be instantiated and called as such:
   * RangeFreqQuery obj = new RangeFreqQuery(arr);
   * int param_1 = obj.query(left,right,value);
   */
  

• class RangeFreqQuery {
  public:
      unordered_map<int, vector<int>> mp;
      RangeFreqQuery(vector<int>& arr) {
          for (int i = 0; i < arr.size(); ++i)
              mp[arr[i]].push_back(i);
      }
  
      int query(int left, int right, int value) {
          if (!mp.count(value)) return 0;
          auto& arr = mp[value];
          auto l = upper_bound(arr.begin(), arr.end(), left - 1);
          auto r = upper_bound(arr.begin(), arr.end(), right);
          return r - l;
      }
  };
  
  /**
   * Your RangeFreqQuery object will be instantiated and called as such:
   * RangeFreqQuery* obj = new RangeFreqQuery(arr);
   * int param_1 = obj->query(left,right,value);
   */
  

• class RangeFreqQuery:
      def __init__(self, arr: List[int]):
          self.mp = defaultdict(list)
          for i, x in enumerate(arr):
              self.mp[x].append(i)
  
      def query(self, left: int, right: int, value: int) -> int:
          if value not in self.mp:
              return 0
          arr = self.mp[value]
          l, r = bisect_right(arr, left - 1), bisect_right(arr, right)
          return r - l
  
  
  # Your RangeFreqQuery object will be instantiated and called as such:
  # obj = RangeFreqQuery(arr)
  # param_1 = obj.query(left,right,value)
  
  

• type RangeFreqQuery struct {
  	mp map[int][]int
  }
  
  func Constructor(arr []int) RangeFreqQuery {
  	mp := make(map[int][]int)
  	for i, v := range arr {
  		mp[v] = append(mp[v], i)
  	}
  	return RangeFreqQuery{mp}
  }
  
  func (this *RangeFreqQuery) Query(left int, right int, value int) int {
  	arr := this.mp[value]
  	l := sort.SearchInts(arr, left)
  	r := sort.SearchInts(arr, right+1)
  	return r - l
  }
  
  /**
   * Your RangeFreqQuery object will be instantiated and called as such:
   * obj := Constructor(arr);
   * param_1 := obj.Query(left,right,value);
   */
  

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