Question:

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”.

Thinking:

The file system is like a tree, and finding path of this tree is like a dfs process. So we can use stack to track the node of dfs. If the string is “..”, we go back, otherwise go to the given dirctory.

Solution:

public String simplifyPath(String path) {
    Stack<String> stack = new Stack<String>();
    String[] paths = path.split("/");

    for (String p: paths) {
        p = p.trim();
        if (p.equals("") || p.equals("."))    continue;
        if (p.equals(".."))    {
            if (!stack.isEmpty()) {
                stack.pop();
            }
            continue;
        }
        stack.push(p);
    }

    StringBuilder res = new StringBuilder();
    while (!stack.isEmpty()) 
        res.insert(0, "/".concat(stack.pop()));


    return res.length() == 0? "/":res.toString();
}