153.Longest Absolute File Path

Suppose we abstract our file system by a string in the following manner:

The string "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext" represents:

dir    subdir1    subdir2        file.ext

The directory dir contains an empty sub-directory subdir1 and a sub-directory subdir2 containing a file file.ext.

The string "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext" represents:

dir    subdir1        file1.ext        subsubdir1    subdir2        subsubdir2            file2.ext

The directory dir contains two sub-directories subdir1 and subdir2. subdir1 contains a file file1.ext and an empty second-level sub-directory subsubdir1. subdir2contains a second-level sub-directory subsubdir2 containing a file file2.ext.

We are interested in finding the longest (number of characters) absolute path to a file within our file system. For example, in the second example above, the longest absolute path is"dir/subdir2/subsubdir2/file2.ext", and its length is 32 (not including the double quotes).

Given a string representing the file system in the above format, return the length of the longest absolute path to file in the abstracted file system. If there is no file in the system, return 0.

Note:

• The name of a file contains at least a . and an extension.
• The name of a directory or sub-directory will not contain a ..

Time complexity required: O(n) where n is the size of the input string.

Notice that a/aa/aaa/file1.txt is not the longest file path, if there is another path aaaaaaaaaaaaaaaaaaaaa/sth.png.

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定义一个链表来存储当前的路径。
         定义一个longest表示当前找到的最长的路径的长度。
         链表中的元素为新建的一个内部类，该内部类有两个属性，level和value。分别存储该文件的路径层次(从0开始统计)，value表示文件名。
         Step1：首先把字符串以"\n"分割成字符数组;
         Step2：如果后面没有元素了则结束，否则继续依次读后面的，读到之后首先生成一个新的element对象currentfile；
         Step3：从链表后面开始倒序读，把level大于等于currentfile的节点都从链表中删除；
         Step4：把currentfile结点加入到链表中;
         Step5：如果currentfile是文件(如file.ext)，则把链表中从头到尾即是该文件的路径，记录下该路径currentpath的长度；如果currentpath的长度比longest大，则更新longest；
         Step6：转到Step2.

  public int LengthLongestPath(string input)        {            if(input.Length == 0)            {                return 0;            }            ArrayList list = new ArrayList();                       string[] arr = Regex.Split(input, "\n", RegexOptions.IgnoreCase);            int len = arr.Length;            /*Step1：首先把字符串以"\n"分割成字符数组;*/            Element current = new Element(arr[0]);           // list.Add(current);            int longest = 0;            /*依次读后面的元素*/            for (int i = 0; i < len;i++ )            {                current = new Element(arr[i]);                /*从链表后面开始倒序读，把level大于等于currentfile的节点都从链表中删除；*/                for (int j = list.Count-1; j >= 0;j-- )                {                   Element e = (Element)list[j];                   if (e.level >= current.level)                   {                       list.RemoveAt(j);                   }                   else {                       break;                   }                }                /*把currentfile结点加入到链表中；*/                list.Add(current);                /*如果currentfile是文件(如file.ext)，则把链表中从头到尾即是该文件的路径，记录下该路径currentpath；*/                if(current.value.Contains(".")){                    StringBuilder temp = new StringBuilder();                    Element node = (Element)list[0];                    temp.Append(node.value);                    for (int k = 1; k < list.Count;k++ )                    {                       node = (Element)list[k];                       temp.Append("/");                       temp.Append(node.value);                    }                    /*如果currentpath的长度比longestpath长，则更新longestpath；*/                    if (temp.Length > longest)                    {                        longest = temp.Length;                    }                }            }            return longest;        }        /**         * 表示存到链表中的元素         */        class Element {            /*str是类似于这种的\t\tsubsub,需要在这里计算出level和str*/            public Element(string str) {                int index = str.LastIndexOf("\t");                level = index + 1;//计算level，比如\t\t\t\ts计算出来应该是4                value = str.Substring(index+1);            }            public int level;//存储该文件的路径层次(从0开始统计)，value表示文件名            public string value;//value表示文件名                    }