solved reverse-linked-list.

Author: sangbeenmoon

number-of-islands/sangbeenmoon.py

@@ -0,0 +1,29 @@
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        
+        m,n = len(grid[0]), len(grid)
+
+        visited = [[False] * m for _ in range(n)]
+
+        dx = [0,0, -1, 1]
+        dy = [-1,1,0,0]
+
+        def dfs(xx:int, yy:int):
+
+            for d in range(4):
+                nx = xx + dx[d]
+                ny = yy + dy[d]
+
+                if 0 <= nx and nx < m and 0 <= ny and ny < n and grid[ny][nx] == "1":
+                    if not visited[ny][nx]:
+                        visited[ny][nx] = True
+                        dfs(nx, ny)
+        
+        answer = 0
+
+        for y in range(n):
+            for x in range(m):
+                if grid[y][x] == "1" and not visited[y][x]:
+                    answer = answer + 1
+                    dfs(x,y)
+        return answer

reverse-linked-list/sangbeenmoon.py

@@ -0,0 +1,20 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+# 1 -> 2 -> 3 -> 4 -> 5
+# 5 -> 4 -> 3 -> 2 -> 1
+
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+
+        cur = head
+        p = None
+        while cur != None:
+            n = ListNode(cur.val, p)
+            p = n
+            cur = cur.next
+        return p
+        
+