文件路径化简

 

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

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

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".

分析：利用栈来化简。

遇到/和/.不入栈，遇到/..出栈，其他入栈

Stack<String> stk = new Stack<String>();
    static final String DOUBLEDOT = "..";
    static final String SINGLEDOT = ".";
    static final String EMPTY = "";

    public String simplifyPath(String path) {
        int i = 0, j = 0;
        while ((i = j) != -1) {
            j = path.indexOf('/', i + 1);
            String s = path.substring(i, j == -1 ? path.length() : j);
            processPath(stk, s);
            if (j == -1) break;
        }
        StringBuilder res = new StringBuilder();
        while (!stk.isEmpty()) {
            res.insert(0, stk.peek());
            stk.pop();
        }
        return res.toString().isEmpty()?"/":res.toString();
    }

    public void processPath(Stack<String> stk, String s) {
        if (s.equals("/" + SINGLEDOT) || s.equals("/")) {

        } else if (s.equals("/" + DOUBLEDOT)) {
            if (!stk.isEmpty())
                stk.pop();
        } else {
            stk.push(s);
        }