diff --git a/longest-substring-without-repeating-characters/lhc0506.js b/longest-substring-without-repeating-characters/lhc0506.js
new file mode 100644
index 000000000..9e28d120e
--- /dev/null
+++ b/longest-substring-without-repeating-characters/lhc0506.js
@@ -0,0 +1,27 @@
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var lengthOfLongestSubstring = function(s) {
+  let maxLength = 0;
+  const charSet = new Set();
+
+  let start = 0, end = 0;
+
+  while (end < s.length) {
+      if (charSet.has(s[end])) {
+          charSet.delete(s[start]);
+          start += 1;
+          continue;
+      }
+
+      charSet.add(s[end]);
+      end += 1;
+      maxLength = Math.max(maxLength, end - start);
+  }
+
+  return maxLength;
+};
+
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
diff --git a/number-of-islands/lhc0506.js b/number-of-islands/lhc0506.js
new file mode 100644
index 000000000..5e5647832
--- /dev/null
+++ b/number-of-islands/lhc0506.js
@@ -0,0 +1,42 @@
+/**
+ * @param {character[][]} grid
+ * @return {number}
+ */
+var numIslands = function(grid) {
+  const m = grid.length;
+  const n = grid[0].length;
+  const visited = Array.from(new Array(m), () => new Array(n).fill(false));
+  const directions = [[0, 1], [0, -1], [1, 0], [-1, 0]];
+
+  let islandCount = 0;
+
+  for (let i = 0; i < m; i++) {
+      for (let j = 0; j < n; j++) {
+          if (grid[i][j] === '1' && !visited[i][j]) {
+              const queue = [[i, j]];
+              visited[i][j] = true;
+
+              while (queue.length) {
+                  const [y, x] = queue.shift();
+
+                  for (const [dy, dx] of directions) {
+                      const newY = y + dy;
+                      const newX = x + dx;
+
+                      if (newY >= 0 && newY < m && newX >= 0 && newX < n && grid[newY][newX] === '1' && !visited[newY][newX]) {
+                          visited[newY][newX] = true;
+                          queue.push([newY, newX]);
+                      }
+                  }
+              }
+
+              islandCount += 1;
+          }
+      }
+  }
+
+  return islandCount;
+};
+
+// 시간복잡도: O(m * n)
+// 공간복잡도: O(m * n)
diff --git a/reverse-linked-list/lhc0506.js b/reverse-linked-list/lhc0506.js
new file mode 100644
index 000000000..f4577b116
--- /dev/null
+++ b/reverse-linked-list/lhc0506.js
@@ -0,0 +1,28 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var reverseList = function(head) {
+  let prevNode = null;
+  let currentNode = head;
+
+  while(currentNode) {
+      const nextNode = currentNode.next;
+      currentNode.next = prevNode;
+
+      prevNode = currentNode;
+      currentNode = nextNode;
+  }
+
+  return prevNode;
+};
+
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)