diff --git a/leetcode/src/d25/_2563_count_the_number_of_fair_pairs.rs b/leetcode/src/d25/_2563_count_the_number_of_fair_pairs.rs
new file mode 100644
index 0000000..ef0ccaf
--- /dev/null
+++ b/leetcode/src/d25/_2563_count_the_number_of_fair_pairs.rs
@@ -0,0 +1,43 @@
+struct Solution;
+
+fn lower_bound(nums: &[i32], bound: i32) -> i64 {
+    let mut l = 0;
+    let mut r = nums.len() - 1;
+    let mut res = 0;
+    while l < r {
+        let sum = nums[l] + nums[r];
+        if sum < bound {
+            res += r - l;
+            l += 1;
+        } else {
+            r -= 1;
+        }
+    }
+    res as i64
+}
+
+impl Solution {
+    pub fn count_fair_pairs(mut nums: Vec<i32>, lower: i32, upper: i32) -> i64 {
+        nums.sort();
+        lower_bound(&nums, upper + 1) - lower_bound(&nums, lower)
+    }
+}
+
+#[test]
+fn test() {
+    let nums = vec![0, 1, 7, 4, 4, 5];
+    let lower = 3;
+    let upper = 6;
+    let res = 6;
+    assert_eq!(Solution::count_fair_pairs(nums, lower, upper), res);
+    let nums = vec![1, 7, 9, 2, 5];
+    let lower = 11;
+    let upper = 11;
+    let res = 1;
+    assert_eq!(Solution::count_fair_pairs(nums, lower, upper), res);
+    let nums = vec![0, 0, 0, 0, 0, 0];
+    let lower = 0;
+    let upper = 0;
+    let res = 15;
+    assert_eq!(Solution::count_fair_pairs(nums, lower, upper), res);
+}
diff --git a/leetcode/src/d25/mod.rs b/leetcode/src/d25/mod.rs
new file mode 100644
index 0000000..ab90c23
--- /dev/null
+++ b/leetcode/src/d25/mod.rs
@@ -0,0 +1 @@
+mod _2563_count_the_number_of_fair_pairs;
diff --git a/leetcode/src/lib.rs b/leetcode/src/lib.rs
index 514b28a..70910c1 100644
--- a/leetcode/src/lib.rs
+++ b/leetcode/src/lib.rs
@@ -34,6 +34,6 @@ mod d16;
 mod d17;
 mod d18;
 mod d19;
-//
 mod d20;
 mod d21;
+mod d25;