Todo Python app

LeetcodeProblems/Word Ladder LeetCode #127

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+from collections import defaultdict, deque
+
+def ladderLength(beginWord, endWord, wordList):
+    # If endWord not in wordList, impossible
+    word_set = set(wordList)
+    if endWord not in word_set:
+        return 0
+
+    L = len(beginWord)
+
+    # Build pattern -> words mapping, e.g. h*t -> {hot, hit}
+    patterns = defaultdict(list)
+    for word in word_set:
+        for i in range(L):
+            pat = word[:i] + "*" + word[i+1:]
+            patterns[pat].append(word)
+
+    # Standard BFS
+    queue = deque([(beginWord, 1)])  # (current word, steps)
+    visited = set([beginWord])
+
+    while queue:
+        word, steps = queue.popleft()
+        if word == endWord:
+            return steps
+
+        for i in range(L):
+            pat = word[:i] + "*" + word[i+1:]
+            for nei in patterns.get(pat, []):
+                if nei not in visited:
+                    visited.add(nei)
+                    queue.append((nei, steps + 1))
+            # Optional optimization: clear list to reduce re-traversal
+            patterns[pat] = []
+    return 0
+
+
+if __name__ == "__main__":
+    print(ladderLength("hit", "cog", ["hot","dot","dog","lot","log","cog"]))  # 5: hit -> hot -> dot -> dog -> cog
+    print(ladderLength("hit", "cog", ["hot","dot","dog","lot","log"]))        # 0 (endWord not present)
+    print(ladderLength("a", "c", ["a","b","c"]))                              # 2: a -> c (via b or direct depending on list)

todo.py

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+import json
+import os
+
+DATA_FILE = "tasks.json"
+
+def load_tasks():
+    if not os.path.exists(DATA_FILE):
+        return []
+    try:
+        with open(DATA_FILE, "r", encoding="utf-8") as f:
+            return json.load(f)
+    except (json.JSONDecodeError, OSError):
+        return []
+
+def save_tasks(tasks):
+    with open(DATA_FILE, "w", encoding="utf-8") as f:
+        json.dump(tasks, f, ensure_ascii=False, indent=2)
+
+def list_tasks(tasks):
+    if not tasks:
+        print("No tasks.")
+        return
+    for i, t in enumerate(tasks, 1):
+        status = "✔" if t["done"] else "✗"
+        print(f"{i}. [{status}] {t['title']}")
+
+def add_task(tasks, title):
+    title = title.strip()
+    if not title:
+        print("Title cannot be empty.")
+        return
+    tasks.append({"title": title, "done": False})
+    save_tasks(tasks)
+    print("Added.")
+
+def toggle_task(tasks, index):
+    if index < 1 or index > len(tasks):
+        print("Invalid task number.")
+        return
+    tasks[index - 1]["done"] = not tasks[index - 1]["done"]
+    save_tasks(tasks)
+    print("Updated.")
+
+def delete_task(tasks, index):
+    if index < 1 or index > len(tasks):
+        print("Invalid task number.")
+        return
+    tasks.pop(index - 1)
+    save_tasks(tasks)
+    print("Deleted.")
+
+def help_menu():
+    print("Commands:")
+    print("  list                Show tasks")
+    print("  add <title>         Add a task")
+    print("  done <num>          Toggle done/undone")
+    print("  del <num>           Delete a task")
+    print("  help                Show this help")
+    print("  quit                Exit")
+
+def main():
+    tasks = load_tasks()
+    print("Simple To-Do List")
+    help_menu()
+    while True:
+        try:
+            cmd = input("> ").strip()
+        except (EOFError, KeyboardInterrupt):
+            print("\nBye!")
+            break
+
+        if not cmd:
+            continue
+
+        parts = cmd.split(maxsplit=1)
+        action = parts[0].lower()
+
+        if action == "list":
+            list_tasks(tasks)
+        elif action == "add":
+            if len(parts) == 1:
+                print("Usage: add <title>")
+            else:
+                add_task(tasks, parts[1])
+        elif action == "done":
+            if len(parts) == 1 or not parts[1].isdigit():
+                print("Usage: done <num>")
+            else:
+                toggle_task(tasks, int(parts[1]))
+        elif action == "del":
+            if len(parts) == 1 or not parts[1].isdigit():
+                print("Usage: del <num>")
+            else:
+                delete_task(tasks, int(parts[1]))
+        elif action == "help":
+            help_menu()
+        elif action == "quit":
+            print("Bye!")
+            break
+        else:
+            print("Unknown command. Type 'help'.")
+
+if __name__ == "__main__":
+    main()