diff --git a/problem-1/sortLSD.test.js b/problem-1/sortLSD.test.js
index 0299913..e1eff09 100644
--- a/problem-1/sortLSD.test.js
+++ b/problem-1/sortLSD.test.js
@@ -1,4 +1,32 @@
 const sortLSD = (words, w = words.length) => {
+  const N = words.length;
+  const R = 256;
+  const aux = [];
+
+  for (let d = w - 1; d >= 0; d--) {
+    const count = new Array(R + 1).fill(0);
+
+    // 빈도수
+    // words[i].charCodeAt(d) 현재 단어 위치
+    for (let i = 0; i < N; i++) {
+      count[words[i].charCodeAt(d) + 1]++;
+    }
+
+    // 처음 등장 인덱스
+    for (let i = 0; i < R; i++) {
+      count[i + 1] += count[i];
+    }
+
+    // 임시 배열 분배
+    for (let i = 0; i < N; i++) {
+      aux[count[words[i].charCodeAt(d)]++] = words[i];
+    }
+
+    // 원본 수정
+    for (let i = 0; i < N; i++) {
+      words[i] = aux[i];
+    }
+  }
 };
 
 test('sortLSD는 문자열을 정렬한다.', () => {
diff --git a/problem-1/sortMSD.test.js b/problem-1/sortMSD.test.js
index b3bef71..297978a 100644
--- a/problem-1/sortMSD.test.js
+++ b/problem-1/sortMSD.test.js
@@ -34,6 +34,37 @@ const CUTOFF = 15;
 const charAt = (s, d) => (d < s.length ? s.charCodeAt(d) : -1);
 
 const sort = (words, aux, lo, hi, d) => {
+  // 정렬 범위
+  if (hi <= lo + CUTOFF) {
+    insertionSort(words, lo, hi, d);
+    return;
+  }
+
+  const count = new Array(R + 2).fill(0);
+
+  // 빈도수
+  for (let i = lo; i <= hi; i++) {
+    count[charAt(words[i], d) + 2]++;
+  }
+
+  // 시작 인덱스
+  for (let i = 0; i < R + 1; i++) {
+    count[i + 1] += count[i];
+  }
+
+  // 임시 배열 분해
+  for (let i = lo; i <= hi; i++) {
+    aux[count[charAt(words[i], d) + 1]++] = words[i];
+  }
+
+  // 원본 수정
+  for (let i = lo; i <= hi; i++) {
+    words[i] = aux[i - lo];
+  }
+
+  for (let i = 0; i < R; i++) {
+    sort(words, aux, lo + count[i], lo + count[i + 1] - 1, d + 1);
+  }
 };
 
 const sortMSD = (words) => {
diff --git a/problem-1/sortQuickThree.test.js b/problem-1/sortQuickThree.test.js
index 76ae3f8..c0b351c 100644
--- a/problem-1/sortQuickThree.test.js
+++ b/problem-1/sortQuickThree.test.js
@@ -5,6 +5,32 @@ const exchange = (words, i, j) => {
 };
 
 const sortQuickThree = (words, lo = 0, hi = words.length - 1, d = 0) => {
+  if (hi <= lo) {
+    return;
+  }
+
+  const pivot = charAt(words[lo], d);
+
+  let lt = lo;
+  let gt = hi;
+  let i = lo + 1;
+
+  while (i <= gt) {
+    const t = charAt(words[i], d);
+    if (t < pivot) {
+      exchange(words, lt++, i++);
+    } else if (t > pivot) {
+      exchange(words, i, gt--);
+    } else {
+      i++;
+    }
+  }
+
+  sortQuickThree(words, lo, lt - 1, d);
+  if (pivot >= 0) {
+    sortQuickThree(words, lt, gt, d + 1);
+  }
+  sortQuickThree(words, gt + 1, hi, d);
 };
 
 test('sortQuickThree는 문자열을 정렬한다.', () => {
diff --git a/problem-2/Trie.test.js b/problem-2/Trie.test.js
index 771d8de..a06223f 100644
--- a/problem-2/Trie.test.js
+++ b/problem-2/Trie.test.js
@@ -10,12 +10,57 @@ class Trie {
   #root = new Node();
 
   get(key) {
+    return this.#get(this.#root, key, 0)?.value;
+  }
+
+  #get(node, key, d) {
+    if (!node) {
+      return;
+    }
+
+    if (d === key.length) {
+      return node;
+    }
+
+    const c = key.charCodeAt(d);
+    return this.#get(node.next[c], key, d + 1);
   }
 
   put(key, value) {
+    this.#root = this.#put(this.#root, key, value, 0);
+  }
+
+  #put(node, key, value, d) {
+    if (!node) {
+      node = new Node();
+    }
+
+    if (d === key.length) {
+      node.value = value;
+      return node;
+    }
+
+    const c = key.charCodeAt(d);
+    node.next[c] = this.#put(node.next[c], key, value, d + 1);
+    return node;
   }
 
   size() {
+    return this.#size(this.#root);
+  }
+
+  #size(node) {
+    if (node === undefined) {
+      return 0;
+    }
+
+    let count = node.value !== undefined ? 1 : 0;
+
+    for (let i = 0; i < R; i++) {
+      count += this.#size(node.next[i]);
+    }
+
+    return count;
   }
 
   keys() {
@@ -23,15 +68,108 @@ class Trie {
   }
 
   keysWithPrefix(prefix) {
+    const queue = [];
+    this.#collect(this.#get(this.#root, prefix, 0), prefix, queue);
+    return queue;
+  }
+
+  #collect(node, prefix, queue) {
+    if (node === undefined) {
+      return;
+    }
+
+    if (node.value !== undefined) {
+      queue.push(prefix);
+    }
+
+    for (let i = 0; i < R; i++) {
+      this.#collect(node.next[i], prefix + String.fromCharCode(i), queue);
+    }
   }
 
   keysThatMatch(pattern) {
+    const queue = [];
+    this.#collectWithPattern(this.#root, '', pattern, queue);
+    return queue;
+  }
+
+  #collectWithPattern(node, prefix, pattern, queue) {
+    if (node === undefined) {
+      return;
+    }
+
+    if (node === undefined) {
+      return;
+    }
+
+    if (prefix.length === pattern.length && node.value !== undefined) {
+      queue.push(prefix);
+    }
+
+    if (prefix.length === pattern.length) {
+      return;
+    }
+
+    const next = pattern[prefix.length];
+    for (let i = 0; i < R; i++) {
+      if (next === '.' || next === String.fromCharCode(i)) {
+        this.#collectWithPattern(
+          node.next[i],
+          prefix + String.fromCharCode(i),
+          pattern,
+          queue,
+        );
+      }
+    }
   }
 
   delete(key) {
+    this.#root = this.#delete(this.#root, key, 0);
+  }
+
+  #delete(node, key, d) {
+    if (node === undefined) {
+      return;
+    }
+
+    if (d === key.length) {
+      node.value = undefined;
+    } else {
+      const c = key.charCodeAt(d);
+      node.next[c] = this.#delete(node.next[c], key, d + 1);
+    }
+
+    if (node.value !== undefined) {
+      return node;
+    }
+
+    for (let i = 0; i < R; i++) {
+      if (node.next[i] !== undefined) {
+        return node;
+      }
+    }
   }
 
   longestPrefixOf(query) {
+    const length = this.#search(this.#root, query, 0, 0);
+    return query.substring(0, length);
+  }
+
+  #search(node, query, d, length) {
+    if (node === undefined) {
+      return length;
+    }
+
+    if (node.value !== undefined) {
+      length = d;
+    }
+
+    if (d === query.length) {
+      return length;
+    }
+
+    const c = query.charCodeAt(d);
+    return this.#search(node.next[c], query, d + 1, length);
   }
 }
 
diff --git a/problem-3/repeat-length-encoding.test.js b/problem-3/repeat-length-encoding.test.js
index 42b52ab..77c28c7 100644
--- a/problem-3/repeat-length-encoding.test.js
+++ b/problem-3/repeat-length-encoding.test.js
@@ -1,11 +1,26 @@
 const encode = (words) => {
+  const answer = [];
+
+  for (const input of words) {
+    answer.push(input[0] + input.length);
+  }
+
+  return answer.join('');
 };
 
 const decode = (string) => {
+  const answer = [];
+
+  for (let i = 0; i < string.length - 1; i += 2) {
+    const count = Number(string[i + 1]);
+    answer.push(string[i].repeat(count));
+  }
+
+  return answer;
 };
 
 test('repeat length encoding', () => {
-  const origin = ['a', 'aa', 'aaa', 'aaaa', 'aaaaa', 'aaaaaa', 'aaaaaaaa', 'aaaaaaaa'];
+  const origin = ['a', 'aa', 'aaa', 'aaaa', 'aaaaa', 'aaaaaa', 'aaaaaaa', 'aaaaaaaa'];
 
   const encodedString = encode(origin);