{"id":1351,"date":"2017-12-29T09:37:19","date_gmt":"2017-12-29T17:37:19","guid":{"rendered":"http:\/\/zxi.mytechroad.com\/blog\/?p=1351"},"modified":"2018-10-05T03:11:51","modified_gmt":"2018-10-05T10:11:51","slug":"leetcode-17-letter-combinations-of-a-phone-number","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/searching\/leetcode-17-letter-combinations-of-a-phone-number\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 17. Letter Combinations of a Phone Number"},"content":{"rendered":"<p><iframe loading=\"lazy\" title=\"\u82b1\u82b1\u9171 LeetCode 17. Letter Combinations of a Phone Number - \u5237\u9898\u627e\u5de5\u4f5c EP142\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/fLy8t33M1qQ?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/p>\n<p>\u9898\u76ee\u5927\u610f\uff1a\u7ed9\u4f60\u4e00\u4e32\u7535\u8bdd\u53f7\u7801\uff0c\u8f93\u51fa\u53ef\u4ee5\u7531\u8fd9\u4e32\u7535\u8bdd\u53f7\u7801\u6253\u51fa\u7684\u6240\u6709\u5b57\u7b26\u4e32\u3002<\/p>\n<p><strong>Problem:<\/strong><\/p>\n<p>Given a digit string, return all possible letter combinations that the number could represent.<\/p>\n<p>A mapping of digit to letters (just like on the telephone buttons) is given below.<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/upload.wikimedia.org\/wikipedia\/commons\/thumb\/7\/73\/Telephone-keypad2.svg\/200px-Telephone-keypad2.svg.png\" \/><\/p>\n<pre class=\"decode-attributes:false lang:default decode:true\">Input:Digit string \"23\"\r\nOutput: [\"ad\", \"ae\", \"af\", \"bd\", \"be\", \"bf\", \"cd\", \"ce\", \"cf\"].<\/pre>\n<p><b>Note:<\/b><br \/>\nAlthough the above answer is in lexicographical order, your answer could be in any order you want.<\/p>\n<p><strong>Solution 1: DFS<\/strong><\/p>\n<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">C++<\/h2>\n<div class=\"tabcontent\">\n\n<pre class=\"lang:c++ decode:true\">\/\/ Author: Huahua\r\n\/\/ Runtime: 0 ms\r\nclass Solution {\r\npublic:\r\n    vector&lt;string&gt; letterCombinations(string digits) {\r\n        if (digits.empty()) return {};\r\n        \r\n        vector&lt;vector&lt;char&gt;&gt; d(10);\r\n        d[0] = {' '};\r\n        d[1] = {};\r\n        d[2] = {'a','b','c'};\r\n        d[3] = {'d','e','f'};\r\n        d[4] = {'g','h','i'};\r\n        d[5] = {'j','k','l'};\r\n        d[6] = {'m','n','o'};\r\n        d[7] = {'p','q','r','s'};\r\n        d[8] = {'t','u','v'};\r\n        d[9] = {'w','x','y','z'};\r\n        string cur;\r\n        vector&lt;string&gt; ans;\r\n        dfs(digits, d, 0, cur, ans);\r\n        return ans;\r\n    }\r\nprivate:\r\n    void dfs(const string&amp; digits, \r\n             const vector&lt;vector&lt;char&gt;&gt;&amp; d, \r\n             int l, string&amp; cur, vector&lt;string&gt;&amp; ans) {\r\n        if (l == digits.length()) {\r\n            ans.push_back(cur);\r\n            return;\r\n        }\r\n        \r\n        for (const char c : d[digits[l] - '0']) {\r\n            cur.push_back(c);\r\n            dfs(digits, d, l + 1, cur, ans);\r\n            cur.pop_back();\r\n        }\r\n    }\r\n};<\/pre>\n\n<\/div><h2 class=\"tabtitle\">Java<\/h2>\n<div class=\"tabcontent\">\n\n<pre class=\"lang:java decode:true\">\/\/ Author: Huahua\r\n\/\/ Running time: 3 ms\r\nclass Solution {\r\n    public List&lt;String&gt; letterCombinations(String digits) {      \r\n      String[] d = new String[]{\" \", \r\n                                \"\", \r\n                                \"abc\", \r\n                                \"def\",\r\n                                \"ghi\",\r\n                                \"jkl\",\r\n                                \"mno\",\r\n                                \"pqrs\",\r\n                                \"tuv\",\r\n                                \"wxyz\"};        \r\n      char[] cur = new char[digits.length()];\r\n      List&lt;String&gt; ans = new ArrayList&lt;&gt;();\r\n      dfs(digits, d, 0, cur, ans);\r\n      return ans;\r\n    }\r\n    private void dfs(String digits, String[] d, \r\n                     int l, char[] cur, List&lt;String&gt; ans) {\r\n      if (l == digits.length()) {\r\n          if (l &gt; 0) ans.add(new String(cur));\r\n          return;\r\n      }\r\n\r\n      String s = d[Character.getNumericValue(digits.charAt(l))];\r\n\r\n      for (int i = 0; i &lt; s.length(); ++i) {\r\n          cur[l] = s.charAt(i);\r\n          dfs(digits, d, l + 1, cur, ans);            \r\n      }\r\n    }\r\n}<\/pre>\n\n<\/div><h2 class=\"tabtitle\">Python3<\/h2>\n<div class=\"tabcontent\">\n\n<pre class=\"lang:python decode:true \">\"\"\"\r\nAuthor: Huahua\r\nRunning time: 60 ms\r\n\"\"\"\r\nclass Solution:\r\n    def letterCombinations(self, digits):\r\n      def dfs(digits, d, l, cur, ans):\r\n        if l == len(digits):\r\n          if l &gt; 0: ans.append(\"\".join(cur))\r\n          return\r\n        \r\n        for c in d[ord(digits[l]) - ord('0')]:\r\n            cur[l] = c\r\n            dfs(digits, d, l + 1, cur, ans)\r\n        \r\n      d = [\" \", \"\", \"abc\", \"def\", \"ghi\", \"jkl\", \"mno\", \"pqrs\", \"tuv\",\"wxyz\"]\r\n      cur = [' ' for _ in range(len(digits))]\r\n      ans = []\r\n      dfs(digits, d, 0, cur, ans)\r\n      return ans\r\n<\/pre>\n<\/div><\/div>\n<p><strong>Solution 2:\u00a0 BFS<\/strong><\/p>\n<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">C++<\/h2>\n<div class=\"tabcontent\">\n\n<pre class=\"lang:c++ decode:true \">\/\/ Author: Huahua\r\n\/\/ Runtime: 3 ms\r\nclass Solution {\r\npublic:\r\n    vector&lt;string&gt; letterCombinations(string digits) {\r\n        if (digits.empty()) return {};\r\n        \r\n        vector&lt;vector&lt;char&gt;&gt; d(10);\r\n        d[0] = {' '};\r\n        d[1] = {};\r\n        d[2] = {'a','b','c'};\r\n        d[3] = {'d','e','f'};\r\n        d[4] = {'g','h','i'};\r\n        d[5] = {'j','k','l'};\r\n        d[6] = {'m','n','o'};\r\n        d[7] = {'p','q','r','s'};\r\n        d[8] = {'t','u','v'};\r\n        d[9] = {'w','x','y','z'};\r\n        vector&lt;string&gt; ans{\"\"};\r\n        for (char digit : digits) {\r\n            vector&lt;string&gt; tmp;\r\n            for (const string&amp; s : ans)\r\n               for (char c : d[digit - '0'])\r\n                    tmp.push_back(s + c);\r\n            ans.swap(tmp);\r\n        }\r\n        return ans;\r\n    }\r\n};<\/pre>\n\n<\/div><h2 class=\"tabtitle\">Java<\/h2>\n<div class=\"tabcontent\">\n\n<pre class=\"lang:java decode:true \">\/\/ Author: Huahua\r\n\/\/ Running time: 4 ms\r\nclass Solution {\r\n    public List&lt;String&gt; letterCombinations(String digits) {\r\n      if (digits.length() == 0) return new ArrayList&lt;String&gt;();\r\n      \r\n      String[] d = new String[]{\" \", \r\n                                \"\", \r\n                                \"abc\", \r\n                                \"def\",\r\n                                \"ghi\",\r\n                                \"jkl\",\r\n                                \"mno\",\r\n                                \"pqrs\",\r\n                                \"tuv\",\r\n                                \"wxyz\"};       \r\n      List&lt;String&gt; ans = new ArrayList&lt;&gt;();\r\n      ans.add(\"\");\r\n      for (char digit : digits.toCharArray()) {\r\n        List&lt;String&gt; tmp = new ArrayList&lt;&gt;();\r\n        for (String t : ans) {\r\n          String s = d[Character.getNumericValue(digit)];\r\n          for (int i = 0; i &lt; s.length(); ++i)\r\n            tmp.add(t + s.charAt(i));\r\n        }\r\n        ans = tmp;\r\n      }\r\n      \r\n      return ans;\r\n    }\r\n\r\n}<\/pre>\n\n<\/div><h2 class=\"tabtitle\">Python<\/h2>\n<div class=\"tabcontent\">\n\n<pre class=\"lang:python decode:true \">\"\"\"\r\nAuthor: Huahua\r\nRunning time: 61 ms\r\n\"\"\"\r\nclass Solution:\r\n    def letterCombinations(self, digits):\r\n      if not digits: return []      \r\n      d = [\" \", \"\", \"abc\", \"def\", \"ghi\", \"jkl\", \"mno\", \"pqrs\", \"tuv\",\"wxyz\"]\r\n      ans = [\"\"]\r\n      for digit in digits:\r\n        tmp = []\r\n        for s in ans:\r\n          for c in d[ord(digit) - ord('0')]:\r\n            tmp.append(s + c)\r\n        ans = tmp\r\n      \r\n      return ans\r\n<\/pre>\n<\/div><\/div>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u9898\u76ee\u5927\u610f\uff1a\u7ed9\u4f60\u4e00\u4e32\u7535\u8bdd\u53f7\u7801\uff0c\u8f93\u51fa\u53ef\u4ee5\u7531\u8fd9\u4e32\u7535\u8bdd\u53f7\u7801\u6253\u51fa\u7684\u6240\u6709\u5b57\u7b26\u4e32\u3002 Problem: Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[44],"tags":[34,122,33,177,42],"class_list":["post-1351","post","type-post","status-publish","format-standard","hentry","category-searching","tag-bfs","tag-combination","tag-dfs","tag-medium","tag-search","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/1351","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/comments?post=1351"}],"version-history":[{"count":11,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/1351\/revisions"}],"predecessor-version":[{"id":4156,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/1351\/revisions\/4156"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=1351"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=1351"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=1351"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}