diff --git a/longest-substring-without-repeating-characters/donghyeon95.java b/longest-substring-without-repeating-characters/donghyeon95.java
new file mode 100644
index 000000000..5fd043eba
--- /dev/null
+++ b/longest-substring-without-repeating-characters/donghyeon95.java
@@ -0,0 +1,37 @@
+import java.util.HashMap;
+
+class Solution {
+	public int lengthOfLongestSubstring(String s) {
+		// subString을 찾아야 한다.
+		// for 문을 반복하면서 내가 가지고 있는 문자열에 있는 문자라면
+		// 그 문자열까지의 길이를 기록하고 꼬리를 짜르고 다시 반복문
+		int result = 0;
+		HashMap<String, Boolean> hm = new HashMap<>();
+		StringBuilder nowString = new StringBuilder();
+
+		for (String charater: s.split("")) {
+			System.out.println(charater);
+			if (hm.containsKey(charater)) {
+				// nowString
+				int index = nowString.indexOf(charater);
+				nowString = new StringBuilder(nowString.substring(index+1) + charater);
+				result = Math.max(nowString.length(), result);
+				String removedString = nowString.substring(0, index);
+				// String의 길이는 최대 27 * n
+				for (String c: removedString.split("")) {
+					hm.remove(c);
+				}
+			}
+			else {
+				hm.put(charater, true);
+				nowString.append(charater);
+			}
+		}
+
+
+		return Math.max(nowString.length(), result);
+	}
+}
+
+
+
diff --git a/number-of-islands/donghyeon95.java b/number-of-islands/donghyeon95.java
new file mode 100644
index 000000000..e2e95eed7
--- /dev/null
+++ b/number-of-islands/donghyeon95.java
@@ -0,0 +1,36 @@
+class Solution {
+
+	int[][] moves = {{1,0}, {-1,0}, {0,1}, {0,-1}};
+	boolean[][] visited;
+	public int numIslands(char[][] grid) {
+		// 섬의 갯수 => 0혹은 경계선으로 둘러싸인 것의 갯수
+		// dfs로 탐색
+		int result = 0;
+		visited = new boolean[grid.length][grid[0].length];
+
+		for (int i=0; i<grid.length; i++) {
+			for (int j=0; j<grid[0].length; j++) {
+				if (grid[i][j] == '1' && !visited[i][j]) {
+					dfs(i, j, grid);
+					result++;
+				}
+			}
+		}
+
+		return result;
+	}
+
+	public void dfs(int y, int x, char[][] grid) {
+		visited[y][x] = true;
+
+		for (int[] move: moves) {
+			int newX = x + move[0];
+			int newY = y + move[1];
+
+			if (newX<0 || newX >= grid[0].length || newY<0 || newY >= grid.length || visited[newY][newX] || grid[newY][newX]=='0') continue;
+			dfs(newY, newX, grid);
+		}
+	}
+}
+
+
diff --git a/reverse-linked-list/donghyeon95.java b/reverse-linked-list/donghyeon95.java
new file mode 100644
index 000000000..08ef84089
--- /dev/null
+++ b/reverse-linked-list/donghyeon95.java
@@ -0,0 +1,30 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+
+// 시간 복잡도 : O(n)
+// 공간 복잡도 : O(n)
+class Solution {
+	public ListNode reverseList(ListNode head) {
+		// 반복문을 돌면서 f(x+1)의 next를 f(x)로 지정
+		ListNode result = null;
+
+		while(head != null) {
+			ListNode nextNode = new ListNode(head.val);
+			nextNode.next = result;
+			result = nextNode;
+			head = head.next;
+		}
+
+		return result;
+	}
+}
+
+
diff --git a/set-matrix-zeroes/donghyeon95.java b/set-matrix-zeroes/donghyeon95.java
new file mode 100644
index 000000000..74bf5a745
--- /dev/null
+++ b/set-matrix-zeroes/donghyeon95.java
@@ -0,0 +1,58 @@
+class Solution {
+	public void setZeroes(int[][] matrix) {
+		int rows = matrix.length;
+		int cols = matrix[0].length;
+
+		boolean firstRowHasZero = false;
+		boolean firstColHasZero = false;
+
+		// 1. 첫 번째 행과 열에 0이 있는지 확인
+		for (int i = 0; i < rows; i++) {
+			if (matrix[i][0] == 0) {
+				firstColHasZero = true;
+				break;
+			}
+		}
+		for (int j = 0; j < cols; j++) {
+			if (matrix[0][j] == 0) {
+				firstRowHasZero = true;
+				break;
+			}
+		}
+
+		// 2. 나머지 행렬에서 0 찾기 (첫 번째 행과 열에 기록)
+		for (int i = 1; i < rows; i++) {
+			for (int j = 1; j < cols; j++) {
+				if (matrix[i][j] == 0) {
+					matrix[i][0] = 0; // 해당 행 표시
+					matrix[0][j] = 0; // 해당 열 표시
+				}
+			}
+		}
+
+		// 3. 첫 번째 행과 열의 정보를 기반으로 행렬 수정
+		for (int i = 1; i < rows; i++) {
+			for (int j = 1; j < cols; j++) {
+				if (matrix[i][0] == 0 || matrix[0][j] == 0) {
+					matrix[i][j] = 0;
+				}
+			}
+		}
+
+		// 4. 첫 번째 열 복구
+		if (firstColHasZero) {
+			for (int i = 0; i < rows; i++) {
+				matrix[i][0] = 0;
+			}
+		}
+
+		// 5. 첫 번째 행 복구
+		if (firstRowHasZero) {
+			for (int j = 0; j < cols; j++) {
+				matrix[0][j] = 0;
+			}
+		}
+	}
+}
+
+
diff --git a/unique-paths/donghyeon95.java b/unique-paths/donghyeon95.java
new file mode 100644
index 000000000..4d03a976b
--- /dev/null
+++ b/unique-paths/donghyeon95.java
@@ -0,0 +1,21 @@
+import java.util.Arrays;
+
+class Solution {
+	public int uniquePaths(int m, int n) {
+		// f(x,y) = f(x-1, y) + f(x, y-1)
+		int[][] dp = new int[m][n];
+		Arrays.fill(dp[0], 1);
+		for (int i=0; i<m; i++) {
+			dp[i][0] = 1;
+		}
+
+		for (int i=1; i<m; i++) {
+			for (int j=1; j<n; j++) {
+				dp[i][j] = dp[i-1][j] + dp[i][j-1];
+			}
+		}
+
+		return dp[m - 1][n - 1];
+	}
+}
+