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➤微信公众号：山青咏芝（shanqingyongzhi）
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Given a 2D board and a list of words from the dictionary, find all words in the board.
Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.
Example:
Input: words =["oath","pea","eat","rain"]and board = [ ['o','a','a','n'], ['e','t','a','e'], ['i','h','k','r'], ['i','f','l','v'] ] Output:["eat","oath"]
Note:
You may assume that all inputs are consist of lowercase letters a-z.
给定一个二维网格 board 和一个字典中的单词列表 words，找出所有同时在二维网格和字典中出现的单词。
单词必须按照字母顺序，通过相邻的单元格内的字母构成，其中“相邻”单元格是那些水平相邻或垂直相邻的单元格。同一个单元格内的字母在一个单词中不允许被重复使用。
示例:
输入: words =["oath","pea","eat","rain"]and board = [ ['o','a','a','n'], ['e','t','a','e'], ['i','h','k','r'], ['i','f','l','v'] ] 输出:["eat","oath"]
说明:
你可以假设所有输入都由小写字母 a-z 组成。
提示:
- 你需要优化回溯算法以通过更大数据量的测试。你能否早点停止回溯？
- 如果当前单词不存在于所有单词的前缀中，则可以立即停止回溯。什么样的数据结构可以有效地执行这样的操作？散列表是否可行？为什么？ 前缀树如何？如果你想学习如何实现一个基本的前缀树，请先查看这个问题： 实现Trie（前缀树）。
328ms
1 class TrieNode: CustomStringConvertible { 2 var description: String { 3 return "word:(word) children:(children)" 4 } 5 6 var word: String? = nil 7 var children = [Character:TrieNode]() 8 } 9 10 class TrieTree { 11 let root = TrieNode() 12 13 func insert(_ word:String) { 14 var node: TrieNode? = root 15 for c in word{ 16 guard let _node = node else { 17 continue 18 } 19 if let child = _node.children[c] { 20 node = child 21 } else { 22 node = TrieNode() 23 _node.children[c] = node 24 } 25 } 26 node?.word = word 27 28 // print(root) 29 } 30 31 func hasPrefix(_ prefix:[Character]) -> Bool { 32 var node: TrieNode? = root 33 for c in prefix{ 34 guard let _node = node else { 35 return false 36 } 37 if let child = _node.children[c] { 38 node = child 39 } else { 40 return false 41 } 42 } 43 return true 44 } 45 46 func hasWord(_ word:[Character]) -> Bool { 47 var node: TrieNode? = root 48 for c in word{ 49 guard let _node = node else { 50 return false 51 } 52 if let child = _node.children[c] { 53 node = child 54 } else { 55 return false 56 } 57 } 58 return node?.word == nil ? false : true 59 } 60 } 61 62 63 class Solution { 64 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 65 66 67 let trie = TrieTree() 68 var record = [[Bool]](repeating:[Bool](repeating:false, count:board[0].count), count:board.count) 69 var result = Set<String>() 70 71 72 for word in words { 73 trie.insert(word) 74 } 75 76 for x in 0..<board.count { 77 for y in 0..<board[0].count { 78 guard let node = child(board,trie.root,x,y) else { 79 continue 80 } 81 search(board,&record,node,x,y, &result) 82 } 83 } 84 85 return Array(result) 86 87 } 88 89 func child(_ board: [[Character]],_ node:TrieNode,_ x:Int,_ y:Int) -> TrieNode? { 90 guard x < board.count, x >= 0, y < board[0].count, y >= 0 else { 91 return nil 92 } 93 94 return node.children[board[x][y]] 95 } 96 97 func search (_ board: [[Character]],_ record:inout [[Bool]], _ node:TrieNode,_ x:Int, _ y:Int, _ result:inout Set<String>) { 98 guard x < board.count, x >= 0, y < board[0].count, y >= 0, !record[x][y] else { 99 return 100 } 101 102 // print("(x):(y) (board[x][y])") 103 104 if let word = node.word { 105 result.insert(word) 106 } 107 108 record[x][y] = true 109 110 if let nextNode = child(board,node,x+1,y) { 111 search(board,&record,nextNode,x+1,y, &result) 112 } 113 114 if let nextNode = child(board,node,x-1,y) { 115 search(board,&record,nextNode,x-1,y, &result) 116 } 117 118 if let nextNode = child(board,node,x,y+1) { 119 search(board,&record,nextNode,x,y+1, &result) 120 } 121 122 if let nextNode = child(board,node,x,y-1) { 123 search(board,&record,nextNode,x,y-1, &result) 124 } 125 126 record[x][y] = false 127 } 128 }
348ms
1 class Solution { 2 3 let lowerLetterUnicodeStart = Character("a").char2Int() 4 5 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 6 var board = board 7 var result = [String]() 8 let root = buildTrie(words) 9 let (m, n) = (board.count, board[0].count) 10 11 func dfs(_ i: Int, _ j: Int, _ root: TrieNode) { 12 if i < 0 || j < 0 || i >= m || j >= n { return } 13 let char = board[i][j] 14 let charIndex = char.char2Int() - lowerLetterUnicodeStart 15 if char == "#" || root.next[charIndex] == nil { return } 16 let root = root.next[charIndex]! 17 if let rootWord = root.word { 18 result.append(rootWord) 19 root.word = nil 20 } 21 board[i][j] = "#" 22 dfs(i - 1, j, root) 23 dfs(i, j - 1, root) 24 dfs(i + 1, j, root) 25 dfs(i, j + 1, root) 26 board[i][j] = char 27 } 28 29 for i in 0..<m { 30 for j in 0..<n { 31 dfs(i, j, root) 32 } 33 } 34 return result 35 } 36 37 func buildTrie(_ words: [String]) -> TrieNode { 38 let root = TrieNode() 39 for word in words { 40 var point = root 41 for char in word { 42 let charIndex = char.char2Int() - lowerLetterUnicodeStart 43 if point.next[charIndex] == nil { point.next[charIndex] = TrieNode() } 44 point = point.next[charIndex]! 45 } 46 point.word = word 47 } 48 return root 49 } 50 } 51 52 class TrieNode { 53 var next: [TrieNode?] = Array(repeating: nil, count: 26) 54 var word: String? 55 } 56 57 extension Character { 58 func char2Int() -> Int { 59 return Int(self.unicodeScalars.first!.value) 60 } 61 }
364ms
1 class Solution { 2 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 3 var board = board 4 var trie = Trie() 5 6 for word in words { 7 trie.insert(word) 8 } 9 10 var result = [String]() 11 12 if board.isEmpty { 13 return result 14 } 15 16 for i in 0 ..< board.count { 17 for j in 0 ..< board[0].count { 18 dfs(&board, i, j, trie.root, &result) 19 } 20 } 21 return result 22 } 23 24 func dfs(_ board: inout [[Character]], _ i: Int, _ j: Int, _ trie: TrieNode, _ result: inout [String]) { 25 var trie = trie 26 27 if board[i][j] == "*" || trie.children[board[i][j]] == nil { 28 return 29 } 30 31 trie = trie.children[board[i][j]]! 32 33 if trie.word != "*" { 34 result.append(trie.word) 35 trie.word = "*" 36 } 37 38 var cur = board[i][j] 39 board[i][j] = "*" 40 if (i < board.count-1) { dfs(&board, i+1, j, trie, &result) } 41 if (i > 0) { dfs(&board, i-1, j, trie, &result) } 42 if (j < board[0].count-1) { dfs(&board, i, j+1, trie, &result) } 43 if (j > 0) { dfs(&board, i, j-1, trie, &result) } 44 board[i][j] = cur 45 return 46 } 47 } 48 49 class Trie { 50 public var root = TrieNode() 51 52 public func insert(_ word: String) { 53 var head = root 54 55 for w in word { 56 if head.children[w] == nil { 57 head.children[w] = TrieNode() 58 } 59 60 head = head.children[w]! 61 } 62 head.word = word 63 } 64 } 65 66 class TrieNode { 67 public var word: String = "*" 68 public var children = [Character : TrieNode]() 69 }
384ms
1 class TrieNode { 2 var word: String? = nil 3 var children = [Character:TrieNode]() 4 } 5 6 class TrieTree { 7 let root = TrieNode() 8 9 func insert(_ word:String) { 10 var node: TrieNode? = root 11 for c in word{ 12 guard let _node = node else { 13 continue 14 } 15 if let child = _node.children[c] { 16 node = child 17 } else { 18 node = TrieNode() 19 _node.children[c] = node 20 } 21 } 22 node?.word = word 23 } 24 } 25 26 27 class Solution { 28 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 29 30 31 let trie = TrieTree() 32 var record = [[Bool]](repeating:[Bool](repeating:false, count:board[0].count), count:board.count) 33 var result = Set<String>() 34 35 36 for word in words { 37 trie.insert(word) 38 } 39 40 for x in 0..<board.count { 41 for y in 0..<board[0].count { 42 guard let node = trie.root.children[board[x][y]] else { 43 continue 44 } 45 search(board,&record,node,x,y, &result) 46 } 47 } 48 49 return Array(result) 50 51 } 52 53 54 func search (_ board: [[Character]],_ record:inout [[Bool]], _ node:TrieNode,_ x:Int, _ y:Int, _ result:inout Set<String>) { 55 guard !record[x][y] else { 56 return 57 } 58 59 if let word = node.word { 60 result.insert(word) 61 } 62 63 record[x][y] = true 64 65 for (x,y) in [(x+1,y),(x-1,y),(x,y+1),(x,y-1)] { 66 guard x < board.count, x >= 0, y < board[0].count, y >= 0, let next = node.children[board[x][y]] else { 67 continue 68 } 69 search(board,&record,next,x,y, &result) 70 } 71 72 record[x][y] = false 73 } 74 }
488ms
1 class Solution { 2 let directions = [ 3 [0, 1], 4 [1, 0], 5 [0, -1], 6 [-1, 0], 7 ] 8 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 9 var result = [String]() 10 guard board.count > 0 && board[0].count > 0 && words.count > 0 else { 11 return result 12 } 13 var wordChars = words.map { Array($0) } 14 var root = TrieNode() 15 for chars in wordChars { 16 buildTree(&root, chars) 17 } 18 var board = board 19 for row in 0..<board.count { 20 for col in 0..<board[0].count { 21 doFindWords(&board, &result, row, col, &root) 22 } 23 } 24 return result 25 } 26 27 private func doFindWords(_ board: inout [[Character]], _ result: inout [String], _ row: Int, _ col: Int, _ node: inout TrieNode) { 28 guard 0 <= row && row < board.count && 0 <= col && col < board[0].count else { 29 return 30 } 31 let char = board[row][col] 32 guard node.next[char] != nil else { 33 return 34 } 35 var node = node.next[char]! 36 if let word = node.getWord() { 37 result.append(word) 38 node.setWord(nil) 39 } 40 board[row][col] = "#" 41 for direction in directions { 42 doFindWords(&board, &result, row + direction[0], col + direction[1], &node) 43 } 44 board[row][col] = char 45 } 46 47 private func buildTree(_ root: inout TrieNode, _ chars: [Character]) { 48 var node = root 49 for char in chars { 50 if node.next[char] == nil { 51 node.next[char] = TrieNode() 52 } 53 node = node.next[char]! 54 } 55 node.setWord(String(chars)) 56 } 57 } 58 59 class TrieNode { 60 var next: [Character: TrieNode] 61 var word: String? 62 63 init() { 64 self.next = [Character: TrieNode]() 65 self.word = nil 66 } 67 68 func setWord(_ word: String?) { 69 self.word = word 70 } 71 72 func getWord() -> String? { 73 return word 74 } 75 }
500ms
1 class Solution { 2 private class TrieNode { 3 var children: [TrieNode?] 4 var word: String? 5 6 init() { 7 children = [TrieNode?](repeating: nil, count: 26) 8 word = nil 9 } 10 } 11 12 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 13 var result = [String]() 14 let trieRoot = buildTrie(from: words) 15 let rows = board.count, cols = board[0].count 16 let rowSeen = [Bool](repeating: false, count: cols) 17 var seen = [[Bool]](repeating: rowSeen, count: rows) 18 for r in 0..<rows { 19 for c in 0..<cols { 20 result.append(contentsOf: search(board, &seen, r, c, trieRoot)) 21 } 22 } 23 return result 24 } 25 26 private func buildTrie(from words: [String]) -> TrieNode { 27 let root = TrieNode() 28 for word in words { 29 var node: TrieNode? = root 30 for char in word.unicodeScalars { 31 let index = Int(char.value) - 97 32 if node?.children[index] == nil { 33 node?.children[index] = TrieNode() 34 } 35 node = node?.children[index] 36 } 37 node?.word = word 38 } 39 return root 40 } 41 42 private func search(_ board: [[Character]], _ seen: inout [[Bool]], _ r: Int, _ c: Int, _ node: TrieNode) -> [String] { 43 guard 0 <= r && r < board.count && 0 <= c && c < board[0].count && !seen[r][c] else { 44 return [] 45 } 46 let childNodeIndex = Int(board[r][c].unicodeScalars.first!.value) - 97 47 guard let childNode = node.children[childNodeIndex] else { 48 return [] 49 } 50 var result = [String]() 51 if let word = childNode.word { 52 result.append(word) 53 childNode.word = nil 54 } 55 seen[r][c] = true 56 result.append(contentsOf: search(board, &seen, r + 1, c, childNode)) 57 result.append(contentsOf: search(board, &seen, r - 1, c, childNode)) 58 result.append(contentsOf: search(board, &seen, r, c + 1, childNode)) 59 result.append(contentsOf: search(board, &seen, r, c - 1, childNode)) 60 seen[r][c] = false 61 return result 62 } 63 }
524ms
1 class Solution { 2 3 class WordNode { 4 var children = [WordNode]() 5 var isWord = false 6 var char : Character 7 init(_ c : Character) { 8 char = c 9 } 10 } 11 12 func addWord(_ word : String, _ node : WordNode){ 13 var lastNode = node 14 let wordArr = Array(word) 15 for c in wordArr { 16 var find = false 17 for sub in lastNode.children where sub.char == c { 18 find = true 19 lastNode = sub 20 } 21 22 if !find { 23 let nc = WordNode(c) 24 lastNode.children.append(nc) 25 lastNode = nc 26 } 27 } 28 lastNode.isWord = true 29 } 30 31 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 32 33 let root = WordNode(".") 34 35 for word in words { 36 addWord(word, root) 37 } 38 39 var curr = "" 40 var res = Set<String>() 41 var visited = Array(repeating: Array(repeating: false, count: board[0].count), count: board.count) 42 for i in 0..<board.count { 43 for j in 0..<board[0].count { 44 find(board, &visited, i, j, root, &res, &curr) 45 } 46 } 47 48 return Array(res) 49 } 50 51 func find(_ board : [[Character]], _ visited : inout [[Bool]], _ m : Int, _ n : Int ,_ node : WordNode, _ res : inout Set<String>, _ curr : inout String) { 52 53 54 55 56 let c = board[m][n] 57 var sub : WordNode? 58 for child in node.children where child.char == c { 59 sub = child 60 curr += String(sub!.char) 61 } 62 if sub == nil { 63 return 64 } 65 66 67 if sub!.isWord { 68 res.insert(curr) 69 } 70 71 visited[m][n] = true 72 if m+1 < board.count && !visited[m+1][n] { 73 find(board, &visited, m+1, n, sub!, &res, &curr) 74 } 75 if n+1 < board[0].count && !visited[m][n+1] { 76 find(board, &visited, m, n+1, sub!, &res, &curr) 77 } 78 if m > 0 && !visited[m-1][n] { 79 find(board, &visited, m-1, n, sub!, &res, &curr) 80 } 81 if n > 0 && !visited[m][n-1] { 82 find(board, &visited, m, n-1, sub!, &res, &curr) 83 } 84 visited[m][n] = false 85 curr.popLast() 86 } 87 }
548ms
1 class Node: CustomStringConvertible { 2 var index: Int 3 var char: Character 4 var children = [Node]() 5 6 public var description: String { return "Node: (index) -> (char) & (children.count)" } 7 8 init(_ i: Int, _ c: Character) { 9 index = i 10 char = c 11 } 12 } 13 14 extension String { 15 func charAt(_ i: Int) -> Character { 16 return self[index(startIndex, offsetBy: i)] 17 } 18 } 19 20 class Solution { 21 let abc = (97...122).map({Character(UnicodeScalar($0))}) 22 23 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 24 25 var ans = Set<String>() 26 var m = board.count 27 var n = board[0].count 28 var root = [[Node]]() 29 30 for i in 0..<m { 31 root.append([Node]()) 32 for j in 0..<n { 33 root[i].append(Node((i * n) + j, board[i][j])) 34 } 35 } 36 37 for i in 0..<m { 38 for j in 0..<n { 39 if i > 0 { 40 root[i][j].children.append(root[i - 1][j]) 41 } 42 if i < m - 1 { 43 root[i][j].children.append(root[i + 1][j]) 44 } 45 if j > 0 { 46 root[i][j].children.append(root[i][j - 1]) 47 } 48 if j < n - 1 { 49 root[i][j].children.append(root[i][j + 1]) 50 } 51 } 52 } 53 54 // print(root) 55 56 for word in words { 57 var visited = [Bool](repeating: false, count: m * n) 58 var index = 0 59 60 if (search(root, &visited, String(word.reversed()), &index)) { 61 ans.insert(word) 62 } 63 } 64 65 return Array(ans) 66 } 67 68 func search(_ root: [[Node]], _ visited: inout [Bool], _ word: String, _ index: inout Int) -> Bool { 69 if index == word.count { 70 return true 71 } 72 73 let charToFind = word.charAt(index) 74 var validNodes = [Node]() 75 76 for row in root { 77 for node in row { 78 if node.char == charToFind { 79 if !visited[node.index] { 80 validNodes.append(node) 81 } 82 } 83 } 84 } 85 86 // print(validNodes) 87 88 for node in validNodes { 89 visited[node.index] = true 90 index += 1 91 if searchInWord(node, &visited, word, &index) { 92 return true 93 } 94 index -= 1 95 visited[node.index] = false 96 } 97 98 return false 99 } 100 101 func searchInWord(_ root: Node, _ visited: inout [Bool], _ word: String, _ index: inout Int) -> Bool { 102 if index == word.count { 103 return true 104 } 105 106 let charToFind = word.charAt(index) 107 var validNodes = [Node]() 108 109 for node in root.children { 110 if node.char == charToFind && !visited[node.index] { 111 validNodes.append(node) 112 } 113 } 114 115 for node in validNodes { 116 visited[node.index] = true 117 index += 1 118 if searchInWord(node, &visited, word, &index) { 119 return true 120 } 121 index -= 1 122 visited[node.index] = false 123 } 124 125 return false 126 } 127 }
684ms
1 class Solution { 2 func findWords(_ board: [[Character]], _ words: [String]) -> [String] { 3 //check if board or word is empty 4 if board.count == 0 || board[0].count == 0 || words.count == 0 { 5 return [] 6 } 7 var rowCount = board.count 8 var colCount = board[0].count 9 10 //convert word to a prefix map 11 var isWordMap: [String: Bool] = getWordMap(words) 12 13 //2D array to track visited location 14 var visited = Array(repeating: Array(repeating: false, count: colCount), count: rowCount) 15 16 //result: use set to remove duplicate 17 var wordSet: Set<String> = Set<String>() 18 19 for i in 0 ..< rowCount { 20 for j in 0 ..< colCount { 21 visited[i][j] = true 22 //use word map to find words that be constrcuted from letters 23 findWord(i, j, String(board[i][j]), isWordMap, &visited, &wordSet, board) 24 visited[i][j] = false 25 } 26 } 27 return Array(wordSet) 28 } 29 30 private func getWordMap(_ words: [String]) -> [String: Bool] { 31 var wordMap = [String: Bool]() 32 for word in words { 33 for i in 1 ... word.count { 34 let subString = String(word.prefix(i)) 35 if wordMap[subString] == nil { 36 wordMap[subString] = false 37 } 38 } 39 wordMap[word] = true 40 } 41 return wordMap 42 } 43 44 private func findWord(_ colIndex: Int, _ rowIndex: Int, 45 _ word: String, _ wordMap: [String: Bool], 46 _ visited: inout [[Bool]], _ res: inout Set<String>, 47 _ charBoard: [[Character]]) { 48 //wordMap doesn't contain the prefix, exit 49 if wordMap[word] == nil { 50 return 51 } 52 53 //prefix is word, add to result 54 if wordMap[word]! { 55 res.insert(word) 56 } 57 58 //4 directions 59 let dirX = [0, 0, 1, -1] 60 let dirY = [1, -1, 0, 0] 61 62 for i in 0 ..< 4 { 63 let newCol = colIndex + dirX[i] 64 let newRow = rowIndex + dirY[i] 65 66 //check bounds and if it is visited 67 if !inDict(newCol, newRow, charBoard.count, charBoard[0].count) || visited[newCol][newRow] { 68 continue 69 } 70 71 visited[newCol][newRow] = true 72 //keep checking if word map contains new string 73 findWord(newCol, newRow, word + String(charBoard[newCol][newRow]), 74 wordMap, &visited, &res, charBoard) 75 visited[newCol][newRow] = false 76 } 77 } 78 79 private func inDict(_ colIndex: Int, _ rowIndex: Int, _ colMax: Int, _ rowMax: Int) -> Bool { 80 return colIndex >= 0 && rowIndex >= 0 && colIndex < colMax && rowIndex < rowMax 81 } 82 }