算法描述：

Given an absolute path for a file (Unix-style), simplify it. Or in other words, convert it to the canonical path.

In a UNIX-style file system, a period . refers to the current directory. Furthermore, a double period .. moves the directory up a level. For more information, see: Absolute path vs relative path in Linux/Unix

Note that the returned canonical path must always begin with a slash /, and there must be only a single slash / between two directory names. The last directory name (if it exists) must not end with a trailing /. Also, the canonical path must be the shortest string representing the absolute path.

Example 1:

Input: "/home/"
Output: "/home"
Explanation: Note that there is no trailing slash after the last directory name.

Example 2:

Input: "/../"
Output: "/"
Explanation: Going one level up from the root directory is a no-op, as the root level is the highest level you can go.

Example 3:

Input: "/home//foo/"
Output: "/home/foo"
Explanation: In the canonical path, multiple consecutive slashes are replaced by a single one.
 

Example 4:

Input: "/a/./b/../../c/"
Output: "/c"

Example 5:

Input: "/a/../../b/../c//.//"
Output: "/c"

Example 6:

Input: "/a//b////c/d//././/.."
Output: "/a/b/c"

解題思路：路徑之類的題目，一般都用stack去求解。這個問題需要知道stringstream類和getline方法。

    string simplifyPath(string path) {
        string temp;
        stack<string> stk;
        stringstream ss(path);
        while(getline(ss,temp,‘/‘)){
            if(temp == "." || temp =="") continue;
            else if(temp == ".." && !stk.empty()) stk.pop();
            else if(temp != "..") stk.push(temp);
        }
        string results;
        while(!stk.empty()){
            results = "/" + stk.top() + results;
            stk.pop();
        }
        return results.empty() ? "/" : results;
    }

LeetCode-71-Simplify Path