package q212

type TrieNode struct {
	children [26]*TrieNode
	word     *string
}

func trieIdx(char byte) int8 {
	if char < 'a' || char > 'z' {
		return -1
	}
	return int8(char - 'a')
}

func allocator(bulkSize int) func() *TrieNode {
	var v []TrieNode
	p := 0

	return func() *TrieNode {
		if v == nil || p == bulkSize {
			v = make([]TrieNode, bulkSize)
			p = 0
		}
		p++
		return &v[p-1]
	}
}

func buildTrie(words []string) *TrieNode {
	alloc := allocator(128)
	root := alloc()
	for _, word := range words {
		p := root
		for i := range len(word) {
			idx := trieIdx(word[i])
			if idx < 0 {
				continue
			}
			if p.children[idx] == nil {
				p.children[idx] = alloc()
			}
			p = p.children[idx]
		}
		p.word = &word
	}
	return root
}

type Coord [2]int8

func find(board [][]byte, coord Coord, trie *TrieNode, found *[]string) {
	if coord[0] < 0 || coord[1] < 0 ||
		int(coord[0]) >= len(board) || int(coord[1]) >= len(board[0]) {
		return
	}
	c := board[coord[0]][coord[1]]
	idx := trieIdx(c)
	if idx == -1 || trie.children[idx] == nil {
		return
	}
	// Mark visited
	board[coord[0]][coord[1]] = '.'

	trie = trie.children[idx]
	if trie.word != nil {
		*found = append(*found, *trie.word)
		trie.word = nil // dedup
	}

	find(board, Coord{coord[0] + 1, coord[1]}, trie, found)
	find(board, Coord{coord[0] - 1, coord[1]}, trie, found)
	find(board, Coord{coord[0], coord[1] + 1}, trie, found)
	find(board, Coord{coord[0], coord[1] - 1}, trie, found)
	board[coord[0]][coord[1]] = c
}

func findWords(board [][]byte, words []string) []string {
	trie := buildTrie(words)
	found := []string{}

	for row := range board {
		for col := range board[0] {
			find(board, Coord{int8(row), int8(col)}, trie, &found)
		}
	}
	return found
}

var _ = findWords