July 21, 2025 - Daily Drill¶
🎯 Daily Goals¶
- Review Anki Deck
- Lumosity training
- Leetcode
- Developing laplace
📝 What I learned:¶
Leetcode problem¶
Thinking Process¶
Another backtrack problem. Just iterate through all cells and perform a dfs search on each of them. If there is a match we return True. If none, we return False.
Key Takeaways¶
- Notice sometimes you can reuse the input 2D matrix as a visited matrix. Here you can mark any cell that you have visited as
#. - Remember to restore the visited marker when you backtrack.
Complexity Analysis¶
Denote the number of cells as n and the length of word as L.
Time Complexity: O(n*3LL) Space Complexity: O(L)
We iterate through all cells to perform a DFS. The DFS has at most 3L calculation, since we have three direction to go at each level and there is L level at most. For the space, we only uses the recursion stack which has the same depth as the word.