Added task 2080.

src/main/java/g2001_2100/s2080_range_frequency_queries/RangeFreqQuery.java

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+package g2001_2100.s2080_range_frequency_queries;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class RangeFreqQuery {
+
+ Map<Integer, List<Integer>> map;
+
+ public RangeFreqQuery(int[] arr) {
+ map = new HashMap<>();
+ for (int i = 0; i < arr.length; i++) {
+ if (!map.containsKey(arr[i])) {
+ map.put(arr[i], new ArrayList<>());
+ }
+ map.get(arr[i]).add(i);
+ }
+ }
+
+ public int query(int left, int right, int value) {
+
+ if (!map.containsKey(value)) {
+ return 0;
+ }
+ List<Integer> list = map.get(value);
+ int s = Collections.binarySearch(list, left);
+ int e = Collections.binarySearch(list, right);
+
+ if (s < 0) {
+ s = (s + 1) * (-1);
+ }
+ if (e < 0) {
+ e = (e + 2) * (-1);
+ }
+ return e - s + 1;
+ }
+}
+
+/*
+ * Your RangeFreqQuery object will be instantiated and called as such:
+ * RangeFreqQuery obj = new RangeFreqQuery(arr);
+ * int param_1 = obj.query(left,right,value);
+ */

src/main/java/g2001_2100/s2080_range_frequency_queries/readme.md

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+2080\. Range Frequency Queries
+
+Medium
+
+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:**
+
+* <code>1 <= arr.length <= 10<sup>5</sup></code>
+* <code>1 <= arr[i], value <= 10<sup>4</sup></code>
+* `0 <= left <= right < arr.length`
+* At most <code>10<sup>5</sup></code> calls will be made to `query`

src/test/java/g2001_2100/s2080_range_frequency_queries/RangeFreqQueryTest.java

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+package g2001_2100.s2080_range_frequency_queries;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.Test;
+
+public class RangeFreqQueryTest {
+ @Test
+ public void rangeFreqQuery() {
+ RangeFreqQuery rangeFreqQuery =
+ new RangeFreqQuery(new int[] {12, 33, 4, 56, 22, 2, 34, 33, 22, 12, 34, 56});
+ // return 1. The value 4 occurs 1 time in the subarray [33, 4]
+ assertThat(rangeFreqQuery.query(1, 2, 4), equalTo(1));
+ // return 2. The value 33 occurs 2 times in the whole array.
+ assertThat(rangeFreqQuery.query(0, 11, 33), equalTo(2));
+ }
+}