71. Simplify Path

Description

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".

Solution

Stack, time O(n), space O(n)

没什么难的，注意corner case就行了。

class Solution {
    public String simplifyPath(String path) {
        if (path == null) {
            return null;
        }
        
        String[] tokens = path.split("/");
        Stack<String> stack = new Stack<>();
        
        for (String token : tokens) {
            switch(token.trim()) {
                case "":
                case ".":
                    continue;
                case "..":
                    if (!stack.empty()) {
                        stack.pop();
                    }
                    continue;
                default:
                    stack.push(token);
                    continue;
            }
        }
        
        if (stack.empty()) {
            return "/";
        }
        
        StringBuilder sb = new StringBuilder();
        while (!stack.empty()) {
            sb.insert(0, stack.pop());
            sb.insert(0, "/");
        }
        
        return sb.toString();
    }
}