71. Simplify Path (Stack)

class Solution {
public:
    string simplifyPath(string path) {
        stack<char> pathStack;
        pathStack.push(path[0]);
        for(int i =1; i<path.length(); i++)
        {
            if(path[i]==‘/‘)
            {
                if(pathStack.top() == ‘/‘) continue; //ignore second ‘/‘
                else if(pathStack.top()==‘.‘) //ignore ‘./‘
                {
                    pathStack.pop();
                }
                else
                {
                    pathStack.push(path[i]);
                }
            }
            else if(path[i]==‘.‘)
            {
                if(pathStack.top() != ‘.‘) {
                    pathStack.push(path[i]);
                    continue;
                }
                pathStack.pop(); //pop ‘/..‘中的第一个‘.‘
                if(pathStack.size()==1) continue;
                
                pathStack.pop(); //pop ‘/..‘中的‘/‘
                while(pathStack.top() != ‘/‘) pathStack.pop(); //pop ‘/..‘的上一个文件路径
                if(pathStack.size()>1){
                    pathStack.pop();
                } 
            }
            else
            {
                pathStack.push(path[i]);
            }       
        }
        while(pathStack.size()>1 && (pathStack.top()==‘/‘ || pathStack.top()==‘.‘)) pathStack.pop(); //path最后的‘.‘和‘/‘要去掉

        //stack中剩余的是要return的path
        if(pathStack.empty()) return "/";
        int len = pathStack.size();
        path = path.substr(0,len);
        while(!pathStack.empty())
        {
            path[--len]=pathStack.top();
            pathStack.pop();
        }
        return path;
    }
}