71. Simplify Path

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".

解题思路为stack。

将有效的地址压入stack，若遇到'..'并且stack不为空，则stack.pop()。 最后将简化后的地址以"/"+dir的形式输出。

public class Solution {
    public String simplifyPath(String path) {
        Stack<String> stack = new Stack<>();
        Set<String> skip = new HashSet<>(Arrays.asList("", ".", ".."));
        for(String str : path.split("/")) {
            if(str.equals("..") && !stack.isEmpty()) {
                stack.pop();
            } else if(!skip.contains(str)) {
                stack.push(str);
            }
        }
        String res = stack.isEmpty() ? "/" : "";
        for(String s : stack) {
            res = res + "/" + s;
        }
        return res;
    }
}