leetcode71 Simplify Path

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

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

class Solution { //stack
public:
    string simplifyPath(string path) {
        string ans;
        if(path[0]!='/')
            return ans;
        vector<string> vec;
        int i=0,len=path.length();
        while(i<len)
        {
            int j=i+1;
            while(j<len&&path[j]!='/')
                j++;
            
            string sub=path.substr(i+1,j-i-1);
            if(sub.length()>0)
            {
                if(sub=="..")
                {
                    if(!vec.empty())
                        vec.pop_back();
                }
                else if(sub!=".")
                {
                    vec.push_back(sub);
                }
            }
            i=j;
        }
        if(vec.empty())
            return "/";
        for(int k=0;k<vec.size();k++)
        {
            ans+="/";
            ans+=vec[k];
        }
        return ans;
    }
};