diff --git a/coin-change/yhkee0404.dart b/coin-change/yhkee0404.dart
new file mode 100644
index 0000000000..e0f7458d25
--- /dev/null
+++ b/coin-change/yhkee0404.dart
@@ -0,0 +1,14 @@
+class Solution {
+  int coinChange(List<int> coins, int amount) {
+    List<int> dp = List.filled(amount + 1, amount + 1);
+    // S(n) = O(amount)
+    dp[0] = 0;
+    for (int i = 1; i <= amount; i++) {
+        // T(n) = O(amount * coins.length)
+        dp[i] = 1 + coins.where((x) => x <= i)
+                .map((x) => dp[i - x])
+                .fold(amount, (a, b) => min(a, b));
+    }
+    return dp[amount] <= amount ? dp[amount] : -1;
+  }
+}
diff --git a/find-minimum-in-rotated-sorted-array/yhkee0404.scala b/find-minimum-in-rotated-sorted-array/yhkee0404.scala
new file mode 100644
index 0000000000..3946d5fe0c
--- /dev/null
+++ b/find-minimum-in-rotated-sorted-array/yhkee0404.scala
@@ -0,0 +1,16 @@
+object Solution {
+    def findMin(nums: Array[Int]): Int = {
+        var l = 0
+        var r = nums.size
+        while (l != r) {
+            val m = l + ((r - l) >> 1)
+            // T(n) = lg(n)
+            if (nums(m) <= nums.last) {
+                r = m
+            } else {
+                l = m + 1
+            }
+        }
+        nums(l)
+    }
+}
diff --git a/maximum-depth-of-binary-tree/yhkee0404.rs b/maximum-depth-of-binary-tree/yhkee0404.rs
new file mode 100644
index 0000000000..9ce7351779
--- /dev/null
+++ b/maximum-depth-of-binary-tree/yhkee0404.rs
@@ -0,0 +1,31 @@
+// 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;
+impl Solution {
+    pub fn max_depth(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
+        match root {
+            None => 0,
+            Some(u) => {
+                let u = u.borrow();
+                1 + Self::max_depth(u.left.clone()).max(Self::max_depth(u.right.clone()))
+            }
+        }
+    }
+}
diff --git a/merge-two-sorted-lists/yhkee0404.go b/merge-two-sorted-lists/yhkee0404.go
new file mode 100644
index 0000000000..215e69dd6b
--- /dev/null
+++ b/merge-two-sorted-lists/yhkee0404.go
@@ -0,0 +1,24 @@
+/**
+ * Definition for singly-linked list.
+ * type ListNode struct {
+ *     Val int
+ *     Next *ListNode
+ * }
+ */
+func mergeTwoLists(list1 *ListNode, list2 *ListNode) *ListNode {
+    ans := &ListNode{}
+    l1 := list1
+    l2 := list2
+    l3 := ans
+    for l1 != nil || l2 != nil {
+        if l2 == nil || l1 != nil && l1.Val < l2.Val {
+            l3.Next = l1
+            l1 = l1.Next
+        } else {
+            l3.Next = l2
+            l2 = l2.Next
+        }
+        l3 = l3.Next
+    }
+    return ans.Next
+}
diff --git a/word-search/yhkee0404.kt b/word-search/yhkee0404.kt
new file mode 100644
index 0000000000..493f5c4db4
--- /dev/null
+++ b/word-search/yhkee0404.kt
@@ -0,0 +1,58 @@
+val _DRCS = listOf(
+    listOf(0, -1),
+    listOf(0, 1),
+    listOf(-1, 0),
+    listOf(1, 0),
+)
+
+class Solution {
+    fun exist(board: Array<CharArray>, word: String): Boolean {
+        val offset = 'A'.code
+        val invertedIndex = List('z'.code - offset + 1) {mutableListOf<List<Int>>()}
+        board.withIndex()
+                .forEach { row ->
+                    row.value
+                            .withIndex()
+                            .forEach {
+                                invertedIndex[it.value.toInt() - offset].add(listOf(row.index, it.index))
+                            }
+                }
+        val freq = MutableList(invertedIndex.size) {0}
+        word.map {it.toInt() - offset}
+                .forEach {
+                    freq[it]++
+                }
+        if ((0 until freq.size).any {freq[it] > invertedIndex[it].size}) {
+            return false
+        }
+        val target = if (invertedIndex[word.first().toInt() - offset].size <= invertedIndex[word.last().toInt() - offset].size) word
+        else word.reversed()
+        val stack = invertedIndex[target.first().toInt() - offset].map {
+                    mutableListOf(it.first(), it.last(), 0, 1)
+                }.toMutableList()
+        val visited = MutableList(board.size) {MutableList(board.first().size) {false}}
+        while (! stack.isEmpty()) {
+            val u = stack.last()
+            if (u[2] == 4) {
+                visited[u[0]][u[1]] = false
+                stack.removeLast()
+                continue
+            }
+            if (u[2] == 0) {
+                if (u[3] == target.length) {
+                    return true
+                }
+                visited[u[0]][u[1]] = true
+            }
+            val drc = _DRCS[u[2]]
+            u[2]++
+            val v = mutableListOf(u[0] + drc[0], u[1] + drc[1], 0, u[3] + 1)
+            if (v[0] == -1 || v[0] == board.size || v[1] == -1 || v[1] == board.first().size
+                    || visited[v[0]][v[1]] || board[v[0]][v[1]] != target[u[3]]) {
+                continue
+            }
+            stack.add(v)
+        }
+        return false
+    }
+}