diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index 2ba5ca3..8cd0bc5 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -130,4 +130,7 @@ mod p49_group_anagrams;
 mod p202_happy_number;
 mod p219_contains_duplicate_ii;
 mod p128_longest_consecutive_sequence;
+mod p228_summary_ranges;
+mod p56_merge_intervals;
+mod p57_insert_interval;
 mod p452_minimum_number_of_arrows_to_burst_balloons;
\ No newline at end of file
diff --git a/src/problem/p202_happy_number.rs b/src/problem/p202_happy_number.rs
index e2b33e0..a5d28aa 100644
--- a/src/problem/p202_happy_number.rs
+++ b/src/problem/p202_happy_number.rs
@@ -4,7 +4,7 @@
 pub struct Solution {}
 
 // submission codes start here
-use std::{collections::HashSet, ops::Add};
+use std::collections::HashSet;
 
 impl Solution {
     pub fn is_happy(n: i32) -> bool {
@@ -13,7 +13,6 @@ impl Solution {
         let mut n = Solution::calculate_square(n);
 
         while n != 1 {
-            dbg!(n);
             if s.contains(&n) {
                 return false;
             }
diff --git a/src/problem/p228_summary_ranges.rs b/src/problem/p228_summary_ranges.rs
new file mode 100644
index 0000000..b931932
--- /dev/null
+++ b/src/problem/p228_summary_ranges.rs
@@ -0,0 +1,54 @@
+/**
+ * [228] Summary Ranges
+ */
+pub struct Solution {}
+
+
+// submission codes start here
+
+impl Solution {
+    pub fn summary_ranges(nums: Vec<i32>) -> Vec<String> {
+        let mut result = vec![];
+
+        if nums.len() == 0 {
+            return result;
+        }
+
+        let mut begin = nums[0];
+        let mut end = nums[0];
+
+        for i in 1..nums.len() {
+            if nums[i] == end + 1 {
+                end += 1;
+            } else {
+                result.push(if begin == end {
+                    format!("{}", begin)
+                } else {
+                    format!("{}->{}", begin, end)
+                });
+
+                begin = nums[i];
+                end = nums[i];
+            }
+        }
+
+        result.push(if begin == end {
+            format!("{}", begin)
+        } else {
+            format!("{}->{}", begin, end)
+        });
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_228() {
+    }
+}
diff --git a/src/problem/p56_merge_intervals.rs b/src/problem/p56_merge_intervals.rs
new file mode 100644
index 0000000..026be90
--- /dev/null
+++ b/src/problem/p56_merge_intervals.rs
@@ -0,0 +1,47 @@
+/**
+ * [56] Merge Intervals
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn merge(intervals: Vec<Vec<i32>>) -> Vec<Vec<i32>> {
+        let mut intervals: Vec<(i32, i32)> = intervals.iter().map(|p| (p[0], p[1])).collect();
+
+        intervals.sort_unstable();
+
+        let mut result: Vec<(i32, i32)> = vec![intervals[0]];
+        let mut last = 0;
+
+        for i in 1..intervals.len() {
+            let (begin, end) = intervals[i];
+            let (last_begin, last_end) = result[last];
+
+            if begin <= last_end {
+                result[last].0 = result[last].0.min(begin);
+                result[last].1 = result[last].1.max(end);
+            } else {
+                result.push(intervals[i]);
+                last += 1;
+            }
+        }
+
+        result.iter().map(|p| vec![p.0, p.1]).collect()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_56() {
+        assert_eq!(
+            vec![vec![1, 6], vec![8, 10], vec![15, 18]],
+            Solution::merge(vec![vec![1, 3], vec![2, 6], vec![8, 10], vec![15, 18]])
+        )
+    }
+}
diff --git a/src/problem/p57_insert_interval.rs b/src/problem/p57_insert_interval.rs
new file mode 100644
index 0000000..859ad40
--- /dev/null
+++ b/src/problem/p57_insert_interval.rs
@@ -0,0 +1,49 @@
+/**
+ * [57] Insert Interval
+ */
+pub struct Solution {}
+
+
+// submission codes start here
+
+impl Solution {
+    pub fn insert(intervals: Vec<Vec<i32>>, new_interval: Vec<i32>) -> Vec<Vec<i32>> {
+        let (mut left, mut right) = (new_interval[0], new_interval[1]);
+
+        let mut result = vec![];
+        let mut placed = false;
+
+        for interval in intervals {
+            if interval[1] < left {
+                result.push(interval);
+            } else if interval[0] > right {
+                if !placed {
+                    result.push(vec![left, right]);
+                    placed = true;
+                }
+
+                result.push(interval);
+            } else {
+                left = left.min(interval[0]);
+                right = right.max(interval[1]);
+            }
+        }
+
+        if !placed {
+            result.push(vec![left, right]);
+        }
+
+        result
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_57() {
+    }
+}