DFS notes

When to use dfs? Generally speaking, there are several situations as follows:


Sample answer: combination sum2 


Key Point: 1) sorting before dfs 2) use Index to help remove duplicates 3) consider out of boundary question whenever using arrays

Use DFS without recursion: Use STACK(Every time pop an item, push the it’s children, thus accomplish DFS)

Stack FILO keeps pushing into stack and pop out the newest one. When to use Stack DFS: when we want to get something ITERATIVELY, we can’t do dfs every time to get the next smallest. (sample: BFS iterator)


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