Simplify Path leetcode

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".

"当遇到“/../"则需要返回上级目录，需检查上级目录是否为空。

当遇到"/./"则表示是本级目录，无需做任何特殊操作。 

当遇到"//"则表示是本级目录，无需做任何操作。

当遇到其他字符则表示是文件夹名，无需简化。

当字符串是空或者遇到”/../”，则需要返回一个"/"。

当遇见"/a//b"，则需要简化为"/a/b"。"

所以把字符按照"/" 分出来 如果是"." 或者空(// 分出来是空)不做任何操作
如果是".." 就把arraylist中前一个数删除
如果是其他的就写入arraylist
当最后所有都写入arraylist完之后把arraylist中的string放入一个string中并以"/"相隔
如果最后的string长度为0,  就返回"/"

public class Solution {
    public String simplifyPath(String path) {
        if (path == null || path.length() == 0) {
            return path;
        }
        String[] list = path.split("/");
        ArrayList<String> tem = new ArrayList<String>();
        for (int i = 0; i < list.length; i++) {
            if (list[i].equals(".") || list[i].length() == 0) {
                continue;
            } else if (list[i].equals("..")) {
                if (tem.size() > 0) {
                    tem.remove(tem.size() - 1);
                }
            } else {
                tem.add(list[i]);
            }
        }
        StringBuilder res = new StringBuilder();
        for (String s : tem) {
            res.append("/" + s);
        }
        if (res.length() == 0) {
            return "/";
        } else {
            return res.toString();
        }
    }
}

public class Solution {
    public String simplifyPath(String path) {
        if (path == null || path.length() == 0) {
            return "";
        }
        Stack<String> stack = new Stack<String>();
        String[] list = path.split("/");
        for (String s : list) {
            if (s.equals( ".") || s.length() == 0) {
                continue;
            } else if (s.equals("..")) {
                if (! stack.isEmpty()) {
                    stack.pop();
                }
            } else {
                stack.push(s);
            }
        }
        StringBuilder res = new StringBuilder();
        while (!stack.isEmpty()) {
            String tem = stack.pop();
            res.insert(0, "/" + tem );
        }
        if (res.length() == 0) {
            return "/";
        } else {
        
            return res.toString();
        }
    }
}