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"</pre>

AC代码

class Solution {
public:
    string simplifyPath(string path) {
        vector<string> st;
        for (auto& c : path) if (c == '/') c = ' ';
        istringstream iss(path);
        string word, ans;
        while (iss >> word) {
            if (word == ".") continue;
            else if (word == "..") {
                if (st.empty()) continue;
                st.pop_back();
            }
            else st.push_back(word);
        }
        if (st.empty()) return "/";
        for (auto& ele : st) ans = ans + "/" + ele;       
        return ans;
    }
};

他人代码

class Solution {
public:
    string simplifyPath(string path) {
        string res, t;
        stringstream ss(path);
        vector<string> v;
        while (getline(ss, t, '/')) {
            if (t == "" || t == ".") continue;
            if (t == ".." && !v.empty()) v.pop_back();
            else if (t != "..") v.push_back(t);
        }
        for (string s : v) res += "/" + s;
        return res.empty() ? "/" : res;
    }
};

总结

其实可以不先把所有的‘/’换成空格的，getline函数可以接收第三个参数。
另解抄自：https://www.cnblogs.com/grandyang/p/4347125.html