Given an absolute path for a file (Unix-style), simplify it. 

For example,path = "/home/", => "/home"path = "/a/./b/../../c/", => "/c"path = "/a/../../b/../c//.//", => "/c"path = "/a//b////c/d//././/..", => "/a/b/c"

In a UNIX-style file system, a period ('.') refers to the current directory, so it can be ignored in a simplified path. Additionally, a double period ("..") moves up a directory, so it cancels out whatever the last directory was. For more information, look here: 

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"
  .

居然WA了一上午 還是看標稱的

居然還有/.../這種無恥的路徑

學會了一個新函式

istringstream ss(path);
        while(getline(ss, val, '/')){

class Solution {
public:
    string simplifyPath(string path) {
        vector<string>ans;
        string val;
        istringstream ss(path);
        while(getline(ss, val, '/')){
            if(val==".."){
                if(!ans.empty())
                    ans.erase(ans.end());
            }
            else if(val=="."){
                continue;
            }
            else{
                if(val!="")
                    ans.push_back(val);
            }
        }
        string re="";
        for(int i=0;i<ans.size();i++)
        {
            re+='/';
            re+=ans[i];
        }
        if(re=="")
            re+='/';
        return re;
    }
};