Implement simple string compression where 4 or more identical characters in sequence produces [Character]#[count] in a compressed output string. Consecutive identical characters of count 3 or less are left as-is in the output string. For example:<\/p>\n\n\n\n
ABC -> ABC\nAAABBBCCC -> AAABBBCCC\nAAAABBBBBC -> A#4B#5C\nAAAABBBBBCC -> A#4B#5CC\nAAAABBBBBCCC -> A#4B#5CCC\nAAAABBBBBCCCC -> A#4B#5C#4<\/pre>\n\n\n\nThe approach taken here is to count identical characters in a row and when the current character is different from the previous (or we get to the end of the string), generate more of the output string. If 4 or more identical characters are counted, concatenate to the output string using the #[Count] notation. Otherwise concatenate the actual character 3 or fewer times.
For n characters, the runtime is O(n). Each character in the input loop is visited once. On the output, any identical character sequence produces at most 3 characters on the output.
The output worst case is a string with m identical character sequences of length 3. m * 3 = n chars on the output. So, each input char is visited and n chars are also produced on the output. n inputs + n outputs = 2n total chars = O(n).
Finally, for any input string length n, with one or more identical character sequence where count >= 4, the output string length will be less than n, since any count >= 4 results in its output representation being 3 characters.<\/p>\n\n\n\nfunc encode(_ input: String) -> String {\n \n var count:Int = 0\n var output:String = \"\"\n \n guard var char = input.first else { return \"\" }\n \n for c in input {\n if c == char {\n count = 1 + count\n }\n else {\n output += subencode(char:char, count:count)\n char = c\n count = 1\n }\n }\n\n output += subencode(char:char, count:count)\n\n return output\n}\n\nfunc subencode(char:Character, count:Int) -> String {\n var output = \"\"\n\n if count > 3 {\n output += \"\\(char)#\\(count)\"\n }\n else {\n for _ in 0 ..< count {\n output += \"\\(char)\"\n }\n }\n \n return output\n}\n\nprint(encode(\"\"))\nprint(encode(\"ABC\"))\nprint(encode(\"AAABBBCCC\"))\nprint(encode(\"AAAABBBBBC\"))\nprint(encode(\"AAAABBBBBCC\"))\nprint(encode(\"AAAABBBBBCCC\"))\nprint(encode(\"AAAABBBBBCCCC\"))<\/pre>\n","protected":false},"excerpt":{"rendered":"Implement simple string compression where 4 or more identical characters in sequence produces [Character]#[count] in a compressed output string. Consecutive identical characters of count 3 or less are left as-is in the output string. For example: The approach taken here is to count identical characters in a row and when the current character is different […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"_links":{"self":[{"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/pages\/942"}],"collection":[{"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/resrvoir.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=942"}],"version-history":[{"count":24,"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/pages\/942\/revisions"}],"predecessor-version":[{"id":1000,"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/pages\/942\/revisions\/1000"}],"up":[{"embeddable":true,"href":"https:\/\/resrvoir.com\/index.php?rest_route=\/wp\/v2\/pages\/2"}],"wp:attachment":[{"href":"https:\/\/resrvoir.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=942"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}