diff --git a/best-time-to-buy-and-sell-stock/moonjonghoo.js b/best-time-to-buy-and-sell-stock/moonjonghoo.js
new file mode 100644
index 000000000..9ac0378df
--- /dev/null
+++ b/best-time-to-buy-and-sell-stock/moonjonghoo.js
@@ -0,0 +1,24 @@
+/**
+ * @param {number[]} prices
+ * @return {number}
+ */
+var maxProfit = function (prices) {
+  let minPrices = Infinity;
+  let profit = 0;
+  for (price of prices) {
+    minPrices = Math.min(price, minPrices);
+    profit = Math.max(profit, price - minPrices);
+  }
+  return profit;
+};
+
+var maxProfit = function (prices) {
+  let maxProfit = 0;
+  let currentProfit = 0;
+  for (let i = 1; i < prices.length; i++) {
+    let diff = prices[i] - prices[i - 1];
+    currentProfit = Math.max(0, currentProfit + diff);
+    maxProfit = Math.max(maxProfit, currentProfit);
+  }
+  return maxProfit;
+};
diff --git a/group-anagrams/moonjonghoo.js b/group-anagrams/moonjonghoo.js
new file mode 100644
index 000000000..fbc0f99a8
--- /dev/null
+++ b/group-anagrams/moonjonghoo.js
@@ -0,0 +1,22 @@
+/**
+ * @param {string[]} strs
+ * @return {string[][]}
+ */
+var groupAnagrams = function (strs) {
+  let hashMap = new Map();
+  for (let i = 0; i < strs.length; i++) {
+    let key = strs[i].split("").sort().join("");
+    if (!hashMap.has(key)) {
+      hashMap.set(key, [strs[i]]);
+    } else {
+      hashMap.set(key, [...hashMap.get(key), strs[i]]);
+    }
+  }
+  let answer = [];
+  for ([key, value] of hashMap) {
+    answer.push(value);
+  }
+  return answer.sort((a, b) => a.length - b.length).map((arr) => arr.sort());
+};
+
+console.log(groupAnagrams(["eat", "tea", "tan", "ate", "nat", "bat"]));
diff --git a/word-break/moonjonghoo.js b/word-break/moonjonghoo.js
new file mode 100644
index 000000000..6d4372b93
--- /dev/null
+++ b/word-break/moonjonghoo.js
@@ -0,0 +1,31 @@
+/**
+ * @param {string} s
+ * @param {string[]} wordDict
+ * @return {boolean}
+ */
+var wordBreak = function (s, wordDict) {
+  const memo = new Map(); // 실패/성공 여부 기억
+  const wordSet = new Set(wordDict); // lookup 최적화
+
+  function canBreak(sub) {
+    if (sub === "") return true;
+
+    if (memo.has(sub)) return memo.get(sub);
+
+    for (let i = 1; i <= sub.length; i++) {
+      const prefix = sub.slice(0, i);
+      if (wordSet.has(prefix)) {
+        const suffix = sub.slice(i);
+        if (canBreak(suffix)) {
+          memo.set(sub, true);
+          return true;
+        }
+      }
+    }
+
+    memo.set(sub, false); // 실패한 경우도 기억
+    return false;
+  }
+
+  return canBreak(s);
+};