2024/11/17 灵茶题单 二分查找

src/main/java/com/cool/ling_cha_mount/binary_search/RangeFreqQuery.java

@@ -0,0 +1,39 @@
+package com.cool.ling_cha_mount.binary_search;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class RangeFreqQuery {
+
+    private final Map<Integer, List<Integer>> map = new HashMap<>();
+
+    public RangeFreqQuery(int[] arr) {
+        for (int i = 0; i < arr.length; i++) {
+            map.computeIfAbsent(arr[i], k -> new ArrayList<>()).add(i);
+        }
+    }
+
+    public int query(int left, int right, int value) {
+        List<Integer> list = map.get(value);
+        if (list == null) {
+            return 0;
+        }
+        return binarySearch(list, right + 1) - binarySearch(list, left);
+    }
+
+    private int binarySearch(List<Integer> list, int target) {
+        int left = 0;
+        int right = list.size() - 1;
+        while (left <= right) {
+            int mid = (right - left) / 2 + left;
+            if (list.get(mid) >= target) {
+                right = mid - 1;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return left;
+    }
+}