diff --git a/src/main/java/com/cool/ling_cha_mount/binary_search/Num2563.java b/src/main/java/com/cool/ling_cha_mount/binary_search/Num2563.java
new file mode 100644
index 0000000..51c6927
--- /dev/null
+++ b/src/main/java/com/cool/ling_cha_mount/binary_search/Num2563.java
@@ -0,0 +1,31 @@
+package com.cool.ling_cha_mount.binary_search;
+
+import java.util.Arrays;
+
+public class Num2563 {
+
+    public long countFairPairs(int[] nums, int lower, int upper) {
+        long res = 0;
+        Arrays.sort(nums);
+        for (int i = 0; i < nums.length; i++) {
+            int m = lowerBound(nums, i, upper - nums[i] + 1);
+            int n = lowerBound(nums, i, lower - nums[i]);
+            res += m - n;
+        }
+        return res;
+    }
+
+    private int lowerBound(int[] nums, int right, int target) {
+        int left = -1;
+        while (left + 1 < right) {
+            int mid = (left + right) >>> 1;
+            if (nums[mid] < target) {
+                left = mid;
+            } else {
+                right = mid;
+            }
+        }
+        return right;
+    }
+
+}