let 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".

主题思想： 最初的想法就是利用栈结构，因为有当前目录和上一级目录， 看到了一些边界案例，进行一些细节处理。最后输出从头输出，又并非标准的栈结构，或者说是一个双向栈结构
这里利用List 可以实现，List可以很方便的实现。

class Solution {
    public String simplifyPath(String path) {

        String [] paths=path.split("/");
        List<String> ans=new ArrayList<String>();

        for(int i=0;i<paths.length;i++){
            if(paths[i].length()==0||paths[i].equals(".")) continue;
            else if(paths[i].equals("..")){
                if(ans.size()>0){
                    ans.remove(ans.size()-1);
                }
            }else{
                ans.add(paths[i]);
            }
        }
        String ret="";

        for(int i=0;i<ans.size();i++){
            ret=ret+"/"+ans.get(i);
        }
        if(ret.length()==0) return "/";
        else return ret;
    }
}