diff --git a/binary-tree-maximum-path-sum/moonjonghoo.js b/binary-tree-maximum-path-sum/moonjonghoo.js
new file mode 100644
index 000000000..fd42563bc
--- /dev/null
+++ b/binary-tree-maximum-path-sum/moonjonghoo.js
@@ -0,0 +1,17 @@
+var maxPathSum = function (root) {
+  let maxSum = -Infinity;
+
+  function dfs(node) {
+    if (node === null) return 0; // 6) Base Case
+    const left = Math.max(dfs(node.left), 0); // 8) Pruning
+    const right = Math.max(dfs(node.right), 0); // 8) Pruning
+
+    const currentSum = left + node.val + right; // 9) Pivot Sum
+    maxSum = Math.max(maxSum, currentSum); // 7) Global Max
+
+    return node.val + Math.max(left, right); // 10) Return Value
+  }
+
+  dfs(root); // 4) DFS 시작
+  console.log(maxSum); // 최종 답 출력
+};
diff --git a/merge-intervals/moonjonghoo.js b/merge-intervals/moonjonghoo.js
new file mode 100644
index 000000000..589c6f171
--- /dev/null
+++ b/merge-intervals/moonjonghoo.js
@@ -0,0 +1,21 @@
+function merge(intervals) {
+  if (intervals.length === 0) return [];
+
+  // 1) 시작점 기준 정렬
+  intervals.sort((a, b) => a[0] - b[0]);
+
+  const merged = [];
+  for (const interval of intervals) {
+    // 2) 결과 배열의 마지막 구간
+    const last = merged[merged.length - 1];
+
+    // 3) 겹치지 않으면 새 구간 추가
+    if (!last || interval[0] > last[1]) {
+      merged.push(interval);
+    } else {
+      // 4) 겹치면 병합: 끝점 확장
+      last[1] = Math.max(last[1], interval[1]);
+    }
+  }
+  return merged;
+}
diff --git a/number-of-connected-components-in-an-undirected-graph/moonjonghoo.js b/number-of-connected-components-in-an-undirected-graph/moonjonghoo.js
new file mode 100644
index 000000000..cbea5e8b1
--- /dev/null
+++ b/number-of-connected-components-in-an-undirected-graph/moonjonghoo.js
@@ -0,0 +1,30 @@
+// Time Complexity: O(n + e) — 노드 n개와 간선 e개를 한 번씩 순회
+// Space Complexity: O(n + e) — 인접 리스트 저장 O(n+e), 재귀 호출 스택 최악 O(n)
+function countComponents(n, edges) {
+  // 인접 리스트 생성
+  const adj = Array.from({ length: n }, () => []);
+  for (const [u, v] of edges) {
+    adj[u].push(v);
+    adj[v].push(u);
+  }
+
+  const visited = Array(n).fill(false);
+  let count = 0;
+
+  function dfs(u) {
+    visited[u] = true;
+    for (const v of adj[u]) {
+      if (!visited[v]) dfs(v);
+    }
+  }
+
+  // 모든 노드 순회
+  for (let i = 0; i < n; i++) {
+    if (!visited[i]) {
+      count++;
+      dfs(i);
+    }
+  }
+
+  return count;
+}