diff --git a/non-overlapping-intervals/yhkee0404.swift b/non-overlapping-intervals/yhkee0404.swift
new file mode 100644
index 000000000..e87ed8f06
--- /dev/null
+++ b/non-overlapping-intervals/yhkee0404.swift
@@ -0,0 +1,15 @@
+class Solution {
+    func eraseOverlapIntervals(_ intervals: [[Int]]) -> Int {
+        let intervals = intervals.sorted() { $0[1] < $1[1] } // T(n) = S(n) = O(nlogn)
+        var ans = 0
+        var end = -50_000
+        for se in intervals {
+            if se[0] < end {
+                ans += 1
+                continue
+            }
+            end = se[1]
+        }
+        return ans
+    }
+}
diff --git a/number-of-connected-components-in-an-undirected-graph/yhkee0404.kt b/number-of-connected-components-in-an-undirected-graph/yhkee0404.kt
new file mode 100644
index 000000000..e7a71a479
--- /dev/null
+++ b/number-of-connected-components-in-an-undirected-graph/yhkee0404.kt
@@ -0,0 +1,35 @@
+class Solution {
+    /**
+     * @param n: the number of vertices
+     * @param edges: the edges of undirected graph
+     * @return: the number of connected components
+     */
+    fun countComponents(n: Int, edges: Array<IntArray>): Int {
+        // write your code here
+        val adj = List(n) {mutableListOf<Int>()}
+        edges.forEach {
+                    adj[it[0]].add(it[1])
+                    adj[it[1]].add(it[0])
+                }
+        val visited = MutableList(n) {false} // T(V, E) = S(V, E) = O(V + E)
+        val stack = mutableListOf<Int>()
+        var ans = 0
+        for (i in 0 until n) {
+            if (visited[i]) {
+                continue
+            }
+            ans++
+            visited[i] = true
+            stack.add(i)
+            while (! stack.isEmpty()) {
+                val u = stack.removeLast()
+                adj[u].filter {! visited[it]}
+                        .forEach {
+                            visited[it] = true
+                            stack.add(it)
+                        }
+            }
+        }
+        return ans
+    }
+}
diff --git a/remove-nth-node-from-end-of-list/yhkee0404.rs b/remove-nth-node-from-end-of-list/yhkee0404.rs
new file mode 100644
index 000000000..ff7de692d
--- /dev/null
+++ b/remove-nth-node-from-end-of-list/yhkee0404.rs
@@ -0,0 +1,36 @@
+// Definition for singly-linked list.
+// #[derive(PartialEq, Eq, Clone, Debug)]
+// pub struct ListNode {
+//   pub val: i32,
+//   pub next: Option<Box<ListNode>>
+// }
+// 
+// impl ListNode {
+//   #[inline]
+//   fn new(val: i32) -> Self {
+//     ListNode {
+//       next: None,
+//       val
+//     }
+//   }
+// }
+impl Solution {
+    pub fn remove_nth_from_end(head: Option<Box<ListNode>>, n: i32) -> Option<Box<ListNode>> {
+        let mut dummy = Some(Box::new(ListNode::new(0)));
+        dummy.as_mut().unwrap().next = head;
+        Self::solve(&mut dummy, n);
+        dummy.unwrap().next
+    }
+    fn solve(head: &mut Option<Box<ListNode>>, n: i32) -> i32 {
+        match head {
+            None => 0,
+            Some(u) => {
+                let ans = Self::solve(&mut u.next, n) + 1;
+                if ans == n + 1 {
+                    u.next = u.next.as_mut().unwrap().next.take();
+                }
+                ans
+            }
+        }
+    }
+}
diff --git a/same-tree/yhkee0404.scala b/same-tree/yhkee0404.scala
new file mode 100644
index 000000000..c1f4376fe
--- /dev/null
+++ b/same-tree/yhkee0404.scala
@@ -0,0 +1,20 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null) {
+ *   var value: Int = _value
+ *   var left: TreeNode = _left
+ *   var right: TreeNode = _right
+ * }
+ */
+object Solution {
+    def isSameTree(p: TreeNode, q: TreeNode): Boolean = {
+        return p == null && q == null
+                || (
+                    p != null
+                    && q != null
+                    && p.value == q.value
+                    && this.isSameTree(p.left, q.left)
+                    && this.isSameTree(p.right, q.right)
+                )
+    }
+}
diff --git a/serialize-and-deserialize-binary-tree/yhkee0404.go b/serialize-and-deserialize-binary-tree/yhkee0404.go
new file mode 100644
index 000000000..f2da5a9ba
--- /dev/null
+++ b/serialize-and-deserialize-binary-tree/yhkee0404.go
@@ -0,0 +1,73 @@
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+type Codec struct {
+    
+}
+
+func Constructor() Codec {
+    return Codec{}
+}
+
+// Serializes a tree to a single string.
+func (this *Codec) serialize(root *TreeNode) string {
+    if root == nil {
+        return ""
+    }
+    type Pair struct {
+        node *TreeNode
+        path string
+    }
+    queue := []Pair{{node: root, path: "1"}}
+    var tokens []string
+    for len(queue) != 0 {
+        u := queue[0]
+        queue = queue[1:]
+        tokens = append(tokens, fmt.Sprintf("%s:%d", u.path, u.node.Val))
+        if u.node.Left != nil {
+            queue = append(queue, Pair{node: u.node.Left, path: u.path + "0"})
+        }
+        if u.node.Right != nil {
+            queue = append(queue, Pair{node: u.node.Right, path: u.path + "1"})
+        }
+    }
+    return strings.Join(tokens, ",")
+}
+
+// Deserializes your encoded data to tree.
+func (this *Codec) deserialize(data string) *TreeNode {
+    if data == "" {
+        return nil
+    }
+    nodes := map[string]*TreeNode{}
+    for _, token := range strings.Split(data, ",")  {
+        values := strings.Split(token, ":")
+        path := values[0]
+        nodeVal, _ := strconv.Atoi(values[1])
+        nodes[path] = &TreeNode{Val: nodeVal}
+        if path == "1" {
+            continue
+        }
+        if path[len(path) - 1] == '0' {
+            nodes[path[: len(path) - 1]].Left = nodes[path]
+        } else {
+            nodes[path[: len(path) - 1]].Right = nodes[path]
+        }
+    }
+    return nodes["1"]
+}
+
+
+/**
+ * Your Codec object will be instantiated and called as such:
+ * ser := Constructor();
+ * deser := Constructor();
+ * data := ser.serialize(root);
+ * ans := deser.deserialize(data);
+ */