longest-repeating-character-replacement

Author: i-mprovising

clone-graph/i-mprovising.py

@@ -8,34 +8,36 @@
 
 class Solution:
     def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
+        # dfs
         if not node:
             return 
 
-        clones = {}
-
-        def dfs(node):
-            if node in clones:
-                return clones[node]
-            clone = Node(node.val)
-            clones[node] = clone
-            for nei in node.neighbors:
-                clone.neighbors.append(dfs(nei))
-            return clone
+        clone = Node(node.val)
+        graph = {node:clone}
+        stack = [node]
+        
+        while stack:
+            node = stack.pop()
+            for n in node.neighbors:
+                if n not in graph:
+                    stack.append(n)
+                    graph[n] = Node(n.val)
+                graph[node].neighbors.append(graph[n])
 
-        return dfs(node)
+        return clone
 
     def bfs(self, node):
-          if not node:
+        if not node:
             return
 
-        clone = Node(node.val)
-        clones = {node: clone}
+        clone = Node(node.val) # clone first node
+        clones = {node: clone} # reference node : clone node
         queue = deque([node])
         while queue:
             node = queue.popleft()
             for nei in node.neighbors:
                 if nei not in clones:
-                    clones[nei] = Node(nei.val)
-                    queue.append(nei)
-                clones[node].neighbors.append(clones[nei])
+                    clones[nei] = Node(nei.val) # clone node
+                    queue.append(nei) # append queue neighbor reference node
+                clones[node].neighbors.append(clones[nei]) 
         return clone

longest-repeating-character-replacement/i-mprovising.py

@@ -0,0 +1,24 @@
+from collections import defaultdict
+
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        """
+        Time complexity O(n)
+        Space complexity O(1)
+
+        Sliding window
+        """
+        start, end = 0, 0
+        window = defaultdict(int)
+        max_len = 0
+
+        while end < len(s):
+            window[s[end]] += 1
+            while end-start+1 - max(window.values()) > k:
+                window[s[start]] -= 1
+                start += 1
+            # move idx
+            max_len = max(max_len, end-start+1)
+            end += 1
+
+        return max_len