diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index 9e64e4e..7705b41 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -312,3 +312,5 @@ mod p540_single_element_in_a_sorted_array;
 mod p1547_minimum_cost_to_cut_a_stick;
 
 mod p3258_count_substrings_that_satisfy_k_constraint_i;
+
+mod p3261_count_substrings_that_satisfy_k_constraint_ii;
diff --git a/src/problem/p3261_count_substrings_that_satisfy_k_constraint_ii.rs b/src/problem/p3261_count_substrings_that_satisfy_k_constraint_ii.rs
new file mode 100644
index 0000000..abb952e
--- /dev/null
+++ b/src/problem/p3261_count_substrings_that_satisfy_k_constraint_ii.rs
@@ -0,0 +1,80 @@
+/**
+ * [3261] Count Substrings That Satisfy K-Constraint II
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn count_k_constraint_substrings(s: String, k: i32, queries: Vec<Vec<i32>>) -> Vec<i64> {
+        let s: Vec<u32> = s.chars().map(|x| x.to_digit(10).unwrap()).collect();
+        let n = s.len();
+
+        let mut window = (0, 0);
+        let mut right_array = vec![n; n];
+        let mut prefix = vec![0; n + 1];
+
+        let mut left = 0;
+        for right in 0..n {
+            if s[right] == 0 {
+                window.0 += 1;
+            } else {
+                window.1 += 1;
+            }
+
+            while window.0 > k && window.1 > k {
+                if s[left] == 0 {
+                    window.0 -= 1;
+                } else {
+                    window.1 -= 1;
+                }
+                right_array[left] = right;
+                left += 1;
+            }
+
+            prefix[right + 1] = prefix[right] + (right - left + 1) as i64;
+        }
+
+        queries
+            .into_iter()
+            .map(|query| {
+                let (l, r) = (query[0] as usize, query[1] as usize);
+                let min_r = right_array[l].min(r + 1) as i64;
+                let l = l as i64;
+
+                (min_r - l + 1) * (min_r - l) / 2 + prefix[r + 1] - prefix[min_r as usize]
+            })
+            .collect()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_3261() {
+        assert_eq!(
+            vec![26],
+            Solution::count_k_constraint_substrings("0001111".to_owned(), 2, vec![vec![0, 6]])
+        );
+        assert_eq!(
+            vec![15, 9, 3],
+            Solution::count_k_constraint_substrings(
+                "010101".to_owned(),
+                1,
+                vec![vec![0, 5], vec![1, 4], vec![2, 3]]
+            )
+        );
+        assert_eq!(
+            vec![1, 3, 1],
+            Solution::count_k_constraint_substrings(
+                "00".to_owned(),
+                1,
+                vec![vec![0, 0], vec![0, 1], vec![1, 1]]
+            )
+        );
+    }
+}