[i-mprovising] Week 08 solutions

clone-graph/i-mprovising.py

@@ -0,0 +1,43 @@
+"""
+Time complexity O(V + E)
+Space complexity O(V + E)
+
+DFS, BFS
+"""
+from collections import deque
+
+class Solution:
+    def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
+        # dfs
+        if not node:
+            return 
+
+        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 clone
+
+    def bfs(self, node):
+        if not node:
+            return
+
+        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) # 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

reverse-bits/i-mprovising.py

@@ -0,0 +1,16 @@
+class Solution:
+    """
+    Time, space complexity O(1)
+    """
+    def reverseBits(self, n: int) -> int:
+        stack = []
+        while len(stack) < 32:
+            stack.append(n % 2)
+            n //= 2
+
+        reverse, x = 0, 1 
+        while stack:
+            reverse += stack.pop() * x
+            x *= 2
+
+        return reverse