Simplify Path

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

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

class Solution {
public:
    string simplifyPath(string path) {
        string ret;
        stack<string> stackPath;
        int len = path.length();
        int start = 1;
        if(len <= 1) return path;
        for (int i = 1; i < len; i++) {
            if(path[i] == '/'){
                string str = path.substr(start,i-start);
                start = i+1;
                if(str == ".."){
                    if(!stackPath.empty())
                        stackPath.pop();
                }else if(str == "."){
                    continue;
                }else if(str.length() > 0){
                    stackPath.push(str);
                }
            }
        }
        if (start < len) {
            string str = path.substr(start, len - start);
            if (str == "..") {
                if (!stackPath.empty())
                    stackPath.pop();
            } else if (str != ".") {
                ret = "/" + str;
            }
        }

        while(!stackPath.empty()){
            ret = "/" + stackPath.top() + ret;
            stackPath.pop();
        }
        if(ret.length()==0) ret = "/";
         return ret;
    }
};