diff --git a/longest-substring-without-repeating-characters/parkhojeong.py b/longest-substring-without-repeating-characters/parkhojeong.py
new file mode 100644
index 0000000000..a3f74786a9
--- /dev/null
+++ b/longest-substring-without-repeating-characters/parkhojeong.py
@@ -0,0 +1,22 @@
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        if s == "":
+            return 0
+
+        ch_to_idx = {}
+        start_idx = 0
+
+        i = 0
+        length_of_longest_substring = 1
+        for i in range(len(s)):
+            ch = s[i]
+            if ch in ch_to_idx and ch_to_idx[ch] >= start_idx:
+                start_idx = ch_to_idx[ch] + 1
+                ch_to_idx[ch] = i
+            else:
+                ch_to_idx[ch] = i
+                length_of_substring = i - start_idx + 1
+                length_of_longest_substring = max(length_of_longest_substring, length_of_substring)
+
+        return length_of_longest_substring
+
diff --git a/number-of-islands/parkhojeong.py b/number-of-islands/parkhojeong.py
new file mode 100644
index 0000000000..b6d29e28d4
--- /dev/null
+++ b/number-of-islands/parkhojeong.py
@@ -0,0 +1,26 @@
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        row_len = len(grid)
+        col_len = len(grid[0])
+
+        def dfs(row: int, col: int):
+            if not (0 <= row < row_len and 0 <= col < col_len):
+                return
+
+            if grid[row][col] == "0":
+                return
+
+            grid[row][col] = "0"
+            dfs(row - 1, col)
+            dfs(row + 1, col)
+            dfs(row, col - 1)
+            dfs(row, col + 1)
+
+        num_islands = 0
+        for row in range(row_len):
+            for col in range(col_len):
+                if grid[row][col] == "1":
+                    num_islands += 1
+                    dfs(row, col)
+
+        return num_islands
diff --git a/reverse-linked-list/parkhojeong.py b/reverse-linked-list/parkhojeong.py
new file mode 100644
index 0000000000..6862645954
--- /dev/null
+++ b/reverse-linked-list/parkhojeong.py
@@ -0,0 +1,16 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        prev_node, cur_node = None, head
+
+        while cur_node:
+            next_node = cur_node.next
+
+            cur_node.next = prev_node
+            prev_node, cur_node = cur_node, next_node
+
+        return prev_node
diff --git a/set-matrix-zeroes/parkhojeong.py b/set-matrix-zeroes/parkhojeong.py
new file mode 100644
index 0000000000..0ff8955aec
--- /dev/null
+++ b/set-matrix-zeroes/parkhojeong.py
@@ -0,0 +1,23 @@
+class Solution:
+    def setZeroes(self, matrix: List[List[int]]) -> None:
+        """
+        Do not return anything, modify matrix in-place instead.
+        """
+
+        row_len = len(matrix)
+        col_len = len(matrix[0])
+
+        zero_row_set = set()
+        zero_col_set = set()
+
+        for r in range(row_len):
+            for c in range(col_len):
+                if matrix[r][c] == 0:
+                    zero_row_set.add(r)
+                    zero_col_set.add(c)
+
+        for r in range(row_len):
+            for c in range(col_len):
+                if r in zero_row_set or c in zero_col_set:
+                    matrix[r][c] = 0
+
diff --git a/unique-paths/parkhojeong.py b/unique-paths/parkhojeong.py
new file mode 100644
index 0000000000..87cd9a4a32
--- /dev/null
+++ b/unique-paths/parkhojeong.py
@@ -0,0 +1,10 @@
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        column = [1] * m
+
+        for col in range(n - 1):
+
+            for row in range(1, m):
+                column[row] = column[row] + column[row - 1]
+
+        return column[-1]