diff --git a/binary-tree-level-order-traversal/yhkee0404.rs b/binary-tree-level-order-traversal/yhkee0404.rs
new file mode 100644
index 000000000..ba853c4df
--- /dev/null
+++ b/binary-tree-level-order-traversal/yhkee0404.rs
@@ -0,0 +1,62 @@
+// Definition for a binary tree node.
+// #[derive(Debug, PartialEq, Eq)]
+// pub struct TreeNode {
+//   pub val: i32,
+//   pub left: Option<Rc<RefCell<TreeNode>>>,
+//   pub right: Option<Rc<RefCell<TreeNode>>>,
+// }
+// 
+// impl TreeNode {
+//   #[inline]
+//   pub fn new(val: i32) -> Self {
+//     TreeNode {
+//       val,
+//       left: None,
+//       right: None
+//     }
+//   }
+// }
+use std::rc::Rc;
+use std::cell::RefCell;
+
+#[derive(Clone)]
+struct QueueItem {
+    node: Option<Rc<RefCell<TreeNode>>>,
+    dist: i32,
+}
+
+impl Solution {
+    pub fn level_order(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<Vec<i32>> {
+        let mut ans: Vec<Vec<i32>> = vec![];
+        let mut queue: Vec<QueueItem> = vec![QueueItem::new(root, 0)];
+        let mut head = 0;
+        while head != queue.len() { // T(n) = S(n) = O(n)
+            let u = queue[head].clone();
+            head += 1;
+            match u.node {
+                Some(v) => {
+                    let v = v.borrow();
+                    let v_dist = u.dist + 1;
+                    if ans.len() <= u.dist as usize {
+                        ans.push(vec![]);
+                    }
+                    let mut a = ans.last_mut().unwrap();
+                    a.push(v.val);
+                    queue.push(QueueItem::new(v.left.clone(), v_dist));
+                    queue.push(QueueItem::new(v.right.clone(), v_dist));
+                },
+                None => (),
+            }
+        }
+        ans
+    }
+}
+
+impl QueueItem {
+    fn new(node: Option<Rc<RefCell<TreeNode>>>, dist: i32) -> Self {
+        QueueItem {
+            node: node,
+            dist: dist,
+        }
+    }
+}
diff --git a/counting-bits/yhkee0404.swift b/counting-bits/yhkee0404.swift
new file mode 100644
index 000000000..9ca30b985
--- /dev/null
+++ b/counting-bits/yhkee0404.swift
@@ -0,0 +1,9 @@
+class Solution {
+    func countBits(_ n: Int) -> [Int] {
+        var ans = Array(repeating: 0, count: n + 1) // S(n) = O(n)
+        for i in 1..<n+1 { // T(n) = O(n)
+            ans[i] = ans[i >> 1] + (i & 1)
+        }
+        return ans
+    }
+}
diff --git a/house-robber-ii/yhkee0404.scala b/house-robber-ii/yhkee0404.scala
new file mode 100644
index 000000000..4bada0990
--- /dev/null
+++ b/house-robber-ii/yhkee0404.scala
@@ -0,0 +1,17 @@
+object Solution {
+    def rob(nums: Array[Int]): Int = {
+        if (nums.length == 1) {
+            return nums(0)
+        }
+        val dp = Array.fill(nums.length)(Array.fill(2)(0)) // T(n) = S(n) = O(n)
+        dp(0)(1) = nums(0)
+        dp(1)(0) = nums(1)
+        dp(1)(1) = nums(0)
+        for (i <- 2 until nums.length) {
+            for (j <- 0 to 1) {
+                dp(i)(j) = Math.max(dp(i - 1)(j), dp(i - 2)(j) + nums(i))
+            }
+        }
+        Math.max(dp(nums.length - 2)(1), dp(nums.length - 1)(0))
+    }
+}
diff --git a/meeting-rooms-ii/yhkee0404.kt b/meeting-rooms-ii/yhkee0404.kt
new file mode 100644
index 000000000..79c9b5a98
--- /dev/null
+++ b/meeting-rooms-ii/yhkee0404.kt
@@ -0,0 +1,35 @@
+/**
+ * Definition of Interval:
+ * class Interval {
+ *     var start: Int = 0
+ *     var end: Int = 0
+ *     constructor(start: Int, end: Int) {
+ *         this.start = start
+ *         this.end = end
+ *     }
+ * }
+ */
+
+class Solution {
+    /**
+     * @param intervals: an array of meeting time intervals
+     * @return: the minimum number of conference rooms required
+     */
+    fun minMeetingRooms(intervals: List<Interval?>): Int {
+        // Write your code here
+        val points = mutableListOf<List<Int>>()
+        intervals.filterNotNull() // T(n) = O(nlogn)
+                .forEach {
+                    points.add(listOf(it.start, 1,))
+                    points.add(listOf(it.end, -1,))
+                }
+        var ans = 0
+        var cnt = 0
+        points.sortedBy {it[0]} // T(n) = S(n) = O(n)
+                .forEach {
+                    cnt += it[1]
+                    ans = maxOf(ans, cnt,)
+                }
+        return ans
+    }
+}
diff --git a/word-search-ii/yhkee0404.go b/word-search-ii/yhkee0404.go
new file mode 100644
index 000000000..8855b8ab0
--- /dev/null
+++ b/word-search-ii/yhkee0404.go
@@ -0,0 +1,62 @@
+func findWords(board [][]byte, words []string) []string {
+	root := &TrieNode{}
+	for _, w := range words {
+		root.Insert(w)
+	}
+
+	m, n := len(board), len(board[0])
+	results := []string{}
+
+	var dfs func(r, c int, node *TrieNode)
+	dfs = func(r, c int, node *TrieNode) {
+		ch := board[r][c]
+		if ch == '#' {
+			return
+		}
+		idx := ch - 'a'
+		next := node.children[idx]
+		if next == nil {
+			return
+		}
+		if next.word != "" {
+			results = append(results, next.word)
+			next.word = ""
+		}
+
+		board[r][c] = '#'
+		for _, d := range directions {
+			nr, nc := r+d[0], c+d[1]
+			if nr >= 0 && nr < m && nc >= 0 && nc < n {
+				dfs(nr, nc, next)
+			}
+		}
+		board[r][c] = ch
+	}
+
+	for i := 0; i < m; i++ {
+		for j := 0; j < n; j++ {
+			dfs(i, j, root)
+		}
+	}
+
+	return results
+}
+
+type TrieNode struct {
+	children [26]*TrieNode
+	word     string
+}
+
+func (t *TrieNode) Insert(word string) {
+	node := t
+	for _, ch := range word {
+		idx := ch - 'a'
+		if node.children[idx] == nil {
+			node.children[idx] = &TrieNode{}
+		}
+		node = node.children[idx]
+	}
+	node.word = word
+}
+
+var directions = [][]int{{0, 1}, {0, -1}, {1, 0}, {-1, 0}}