LeetCode Online Judge 题目C# 练习 - Simplify Path

Given an absolute path for a file (Unix-style), simplify it.
For example,
path = "/home/", => "/home"
path = "/a/./b/http://www.cnblogs.com/c/", => "/c"
Corner Cases:
Did you consider the case where path = "/../"?
In this case, you should return "/".
Another corner case is the path might contain multiple slashes '/' together, such as "/home//foo/".
In this case, you should ignore redundant slashes and return "/home/foo".

        public static string SimplifyPath(string s)
        {
            string[] arr = s.Split('/');
            Stack<string> stack = new Stack<string>();

            for (int i = 0; i < arr.Length; i++)
            {
                if (arr[i] != "")
                {
                    if (arr[i] == "..")
                    {
                        if (stack.Count > 0)
                            stack.Pop();
                    }
                    else if (arr[i] == ".")
                    {
                    }
                    else
                    {
                        stack.Push(arr[i]);
                    }
                }
            }

            StringBuilder sb = new StringBuilder();

            while (stack.Count > 0)
            {
                sb.Insert(0, "/" + stack.Pop());
            }

            //solve corner case like "/../"
            if (sb.Length == 0)
                sb.Append("/");

            return sb.ToString();
        }

代码分析：

　　把字符串先用Split（'/') 分开。arr[i] == "" 表示多余的斜杠。arr[i] == ".."表示返回上一级，arr[i] == "." 可以忽略它。

　　要记住最后如果结果为空，要加"/"回到根目录。

　　为什么用StringBuilder 而不用 String? StringBuilder是mutable，string 是immutable。 如果多次反复修改字符串，StringBuilder效率高很多。下面这个link是有人测试后的结果，+25000次，string消耗时间706ms， StringBuilder 1ms。

http://blog.eliotpearson.com/c-string-versus-stringbuilder/