leetcode[71]Simplify Path

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

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

click to show corner cases.

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 {
public:
string simplifyPath(string path) 
{
    if(path.empty())return path;
    stack<string> sta;
    string str="";
    for (int i=0;i<path.size();i++)
    {
        if (path[i]=='/')
        {
            if (str=="..")
            {
                if (!sta.empty())
                {
                    sta.pop();
                }
                str="";
            } 
            else if(str==".")
            {
                str="";
            }
            else if(str!="")
            {
                sta.push(str);
                str="";
            }
        } 
        else
        {
            str+=path[i];
        }
    }
    if (str=="..")
    {
        if (!sta.empty())
        {
            sta.pop();
        }
    }
    else if(str!="."&&str!="")
    {
        sta.push(str);
    }
    string res="";
    while(!sta.empty())
    {
        if (res=="") res=sta.top();
        else  res=sta.top()+"/"+res;
        sta.pop();
    }
    res="/"+res;
    return res;
}
/**
string simplifyPath(string path) 
{
    if (path.empty())return path;
    string str="";
    stack<string> stack1;
    for (int i=0;i<path.size();i++)
    {
        if (path[i]=='/')
        {
            if (str=="..")
            {
                if (!stack1.empty())
                {
                    stack1.pop();
                }
            }
            else if(str.size()!=0&&str!=".")
            {
                stack1.push(str);
            }
            str="";
        }
        else
        {
            str+=path[i];
        }
    }
    if (str=="..")
    {
        if (!stack1.empty())
        {
            stack1.pop();
        }
    }
    else if (str.size()!=0&&str!=".")
    {
        stack1.push(str);
    }
    string res="";
    while(!stack1.empty())
    {
         if(res.size()==0)res=stack1.top();
         else res=stack1.top()+'/'+res;
         stack1.pop();
    }
    res="/"+res;
    return res;
}
*/
};