LeetCode: Simplify Path

LeetCode: Simplify Path 

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/**
 * Created by hzhou on 5/7/15. [email protected] Given an absolute path for a file (Unix-style), simplify it.
 * <p/>
 * For example, path = "/home/", => "/home" path = "/a/./b/../../c/", => "/c"
 * <p/>
 * 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".
 */
public class SimplifyPath {
    public String simplifyPath(String path) {
        if (path == null || path.isEmpty()) {
            return "";
        }
        if (!path.startsWith("/")) {
            return null;
        }
        path = path.trim();
        Stack<String> stack = new Stack<String>();
        StringBuilder sb = new StringBuilder();
        String[] splits = path.split("/");
        for (String s : splits) {
            s = s.trim();
            if (isValid(s)) {
                stack.push(s);
            } else if (s.equals("..")) {
                if (!stack.isEmpty()) {
                    stack.pop();
                }
            }
        }
        for (String s : stack) {
            sb.append("/").append(s);
        }
        return sb.toString().isEmpty() ? "/" : sb.toString();
    }
    private boolean isValid(String s) {
        return !(s.isEmpty() || s.equals(".") || s.equals(".."));
    }
}