{"id":260,"date":"2017-09-13T19:58:37","date_gmt":"2017-09-14T02:58:37","guid":{"rendered":"http:\/\/zxi.mytechroad.com\/blog\/?p=260"},"modified":"2018-07-10T18:49:29","modified_gmt":"2018-07-11T01:49:29","slug":"leetcode-451-sort-characters-by-frequency-2","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/hashtable\/leetcode-451-sort-characters-by-frequency-2\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 451. Sort Characters By Frequency"},"content":{"rendered":"<p><iframe loading=\"lazy\" title=\"\u82b1\u82b1\u9171 LeetCode 451. Sort Characters By Frequency  - \u5237\u9898\u627e\u5de5\u4f5c EP53\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/qdpBD0LFgN0?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><strong>Problem:<\/strong><\/p>\n<p>Given a string, sort it in decreasing order based on the frequency of characters.<\/p>\n<p>Example 1:<\/p>\n<p>Input:<br \/>\n&#8220;tree&#8221;<\/p>\n<p>Output:<br \/>\n&#8220;eert&#8221;<\/p>\n<p>Explanation:<br \/>\n&#8216;e&#8217; appears twice while &#8216;r&#8217; and &#8216;t&#8217; both appear once.<br \/>\nSo &#8216;e&#8217; must appear before both &#8216;r&#8217; and &#8216;t&#8217;. Therefore &#8220;eetr&#8221; is also a valid answer.<br \/>\nExample 2:<\/p>\n<p>Input:<br \/>\n&#8220;cccaaa&#8221;<\/p>\n<p>Output:<br \/>\n&#8220;cccaaa&#8221;<\/p>\n<p>Explanation:<br \/>\nBoth &#8216;c&#8217; and &#8216;a&#8217; appear three times, so &#8220;aaaccc&#8221; is also a valid answer.<br \/>\nNote that &#8220;cacaca&#8221; is incorrect, as the same characters must be together.<br \/>\nExample 3:<\/p>\n<p>Input:<br \/>\n&#8220;Aabb&#8221;<\/p>\n<p>Output:<br \/>\n&#8220;bbAa&#8221;<\/p>\n<p>Explanation:<br \/>\n&#8220;bbaA&#8221; is also a valid answer, but &#8220;Aabb&#8221; is incorrect.<br \/>\nNote that &#8216;A&#8217; and &#8216;a&#8217; are treated as two different characters.<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Idea:<\/strong><\/p>\n<p>Counting sort<\/p>\n<p>&nbsp;<\/p>\n<p><strong>Solution 1:\u00a0<\/strong><\/p>\n<p>Sort the string based on element frequency<\/p>\n<pre class=\"lang:c++ decode:true\">\/\/ Author: Huahua\r\n\/\/ Running time: 289 ms\r\nclass Solution {\r\npublic:\r\n    string frequencySort(string&amp; s) {\r\n        array&lt;int, 128&gt; f{0};\r\n        for(char c:s) ++f[c];\r\n        sort(s.begin(), s.end(), [&amp;f] (char a, char b) {\r\n            return f[a] &gt; f[b] || (f[a] == f[b] &amp;&amp; a &gt; b);\r\n        });\r\n        return s;\r\n    }\r\n};<\/pre>\n<pre class=\"lang:default decode:true\">\/\/ Author: Huahua\r\n\/\/ Running time: 139 ms\r\nclass Solution {\r\npublic:\r\n    string frequencySort(string&amp; s) {\r\n        map&lt;char, int&gt; f;\r\n        for(char c:s) ++f[c];\r\n        sort(s.begin(), s.end(), [&amp;f] (char a, char b) {\r\n            return f[a] &gt; f[b] || (f[a] == f[b] &amp;&amp; a &gt; b);\r\n        });\r\n        return s;\r\n    }\r\n};<\/pre>\n<pre class=\"lang:c++ decode:true\">\/\/ Author: Huahua\r\n\/\/ Running time: 29 ms\r\nclass Solution {\r\npublic:\r\n    string frequencySort(string&amp; s) {\r\n        array&lt;int, 128&gt; f{0};\r\n        for(char c:s) ++f[c];\r\n        sort(s.begin(), s.end(), [&amp;f] (char a, char b) {\r\n            return f[a] &gt; f[b] || (f[a] == f[b] &amp;&amp; a &gt; b);\r\n        });        \r\n        return s;\r\n    }\r\n};<\/pre>\n<p>&nbsp;<\/p>\n<p><strong>Solution 2:<\/strong><\/p>\n<p>Counting sort<\/p>\n<pre class=\"lang:default decode:true\">\/\/ Author: Huahua\r\n\/\/ Running time: 12 ms\r\nclass Solution {\r\npublic:\r\n    string frequencySort(const string&amp; s) {\r\n        vector&lt;int&gt; f(128, 0);\r\n        for(char c:s) ++f[c];\r\n        vector&lt;pair&lt;int,char&gt;&gt; v;\r\n        for (int i = 0; i &lt; 128; ++i) {\r\n            if (f[i] &gt; 0) v.emplace_back(f[i], i);\r\n        }\r\n        sort(v.rbegin(), v.rend());\r\n        string ans;\r\n        for(const auto&amp; kv : v) {\r\n            ans.append(kv.first, kv.second);\r\n        }\r\n        return ans;\r\n    }\r\n};<\/pre>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Problem: Given a string, sort it in decreasing order based on the frequency of characters. Example 1: Input: &#8220;tree&#8221; Output: &#8220;eert&#8221; Explanation: &#8216;e&#8217; appears twice&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[70],"tags":[20,79,81,80,78],"class_list":["post-260","post","type-post","status-publish","format-standard","hentry","category-hashtable","tag-array","tag-container","tag-performance","tag-speed","tag-stl","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/260","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=260"}],"version-history":[{"count":6,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/260\/revisions"}],"predecessor-version":[{"id":3073,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/260\/revisions\/3073"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=260"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=260"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=260"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}