diff --git a/best-time-to-buy-and-sell-stock/krokerdile.js b/best-time-to-buy-and-sell-stock/krokerdile.js
new file mode 100644
index 000000000..bcf022aa5
--- /dev/null
+++ b/best-time-to-buy-and-sell-stock/krokerdile.js
@@ -0,0 +1,14 @@
+var maxProfit = function(prices) {
+    let minPrice = Infinity;
+    let maxProfit = 0;
+
+    for (let price of prices) {
+        if (price < minPrice) {
+            minPrice = price; // 더 싼 가격이 나타나면 갱신
+        } else {
+            maxProfit = Math.max(maxProfit, price - minPrice); // 이익 갱신
+        }
+    }
+
+    return maxProfit;
+};
diff --git a/encode-and-decode-strings/krokerdile.js b/encode-and-decode-strings/krokerdile.js
new file mode 100644
index 000000000..529746753
--- /dev/null
+++ b/encode-and-decode-strings/krokerdile.js
@@ -0,0 +1,35 @@
+class Solution {
+    /**
+     * @param {string[]} strs
+     * @returns {string}
+     */
+    encode(strs) {
+        let result = "";
+
+        for (const str of strs) {
+            result += `${str.length}#${str}`;
+        }
+
+        return result;
+    }
+
+    /**
+     * @param {string} str
+     * @returns {string[]}
+     */
+    decode(s) {
+        let result = [];
+        let i = 0;
+        // 5#hello5#world
+        while (i < s.length) {
+            const pos = s.indexOf("#", i);
+            const len = parseInt(s.slice(i, pos));// 5
+            i = pos + 1;
+            const str = s.slice(i, i + len);
+            result.push(str);
+            i += len;
+        }
+        return result;
+    }
+}
+
diff --git a/group-anagrams/krokerdile.js b/group-anagrams/krokerdile.js
new file mode 100644
index 000000000..32f3ff0a5
--- /dev/null
+++ b/group-anagrams/krokerdile.js
@@ -0,0 +1,23 @@
+/**
+ * @param {string[]} strs
+ * @return {string[][]}
+ */
+var groupAnagrams = function(strs) {
+    const dict = new Map();
+
+    strs.forEach(str => {
+        const sorted = str.split('').sort().join('');
+        if (!dict.has(sorted)) {
+            dict.set(sorted, [str]);
+        } else {
+            dict.get(sorted).push(str);
+        }
+    });
+
+    // value 길이 기준 내림차순 정렬
+    const result = [...dict.entries()]
+        .sort((a, b) => b[1].length - a[1].length)
+        .map(([_, group]) => group); // value (즉, 아나그램 그룹)만 꺼냄
+
+    return result;
+};
diff --git a/implement-trie-prefix-tree/krokerdile.js b/implement-trie-prefix-tree/krokerdile.js
new file mode 100644
index 000000000..06c870839
--- /dev/null
+++ b/implement-trie-prefix-tree/krokerdile.js
@@ -0,0 +1,42 @@
+var Trie = function() {
+    this.root = {}; // 루트는 빈 객체로 시작
+};
+
+/** 
+ * @param {string} word
+ * @return {void}
+ */
+Trie.prototype.insert = function(word) {
+    let node = this.root;
+    for (let ch of word) {
+        if (!node[ch]) node[ch] = {};
+        node = node[ch];
+    }
+    node.isEnd = true; // 단어의 끝을 표시
+};
+
+/** 
+ * @param {string} word
+ * @return {boolean}
+ */
+Trie.prototype.search = function(word) {
+    let node = this.root;
+    for (let ch of word) {
+        if (!node[ch]) return false;
+        node = node[ch];
+    }
+    return node.isEnd === true; // 단어의 끝이어야만 true
+};
+
+/** 
+ * @param {string} prefix
+ * @return {boolean}
+ */
+Trie.prototype.startsWith = function(prefix) {
+    let node = this.root;
+    for (let ch of prefix) {
+        if (!node[ch]) return false;
+        node = node[ch];
+    }
+    return true; // 접두사만 매칭되면 true
+};
diff --git a/word-break/krokerdile.js b/word-break/krokerdile.js
new file mode 100644
index 000000000..85d91a186
--- /dev/null
+++ b/word-break/krokerdile.js
@@ -0,0 +1,22 @@
+/**
+ * @param {string} s
+ * @param {string[]} wordDict
+ * @return {boolean}
+ */
+var wordBreak = function(s, wordDict) {
+    const wordSet = new Set(wordDict); // 빠른 검색을 위한 Set
+    const dp = Array(s.length + 1).fill(false);
+    dp[0] = true; // 빈 문자열은 항상 가능
+
+    for (let i = 1; i <= s.length; i++) {
+        for (let j = 0; j < i; j++) {
+            const word = s.slice(j, i);
+            if (dp[j] && wordSet.has(word)) {
+                dp[i] = true;
+                break; // 더 이상 볼 필요 없음
+            }
+        }
+    }
+
+    return dp[s.length];
+};