LeetCode-Simplify Path

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.

Solution:

public class Solution {
    public String simplifyPath(String path) {
        if (path.isEmpty()) return "";

        StringBuilder builder = new StringBuilder();
        builder.append('/');
        int index = 1;
        while (index<path.length()){
            //get the next directory command.
            int next = index;
            while (next<path.length() && path.charAt(next)!='/') next++;
            String dir = path.substring(index,next);
            if (dir.equals(".") || dir.isEmpty()){
                index = next+1;
                continue;
            } else if (dir.equals("..")){
                pathBack(builder);
            } else {
                builder.append(dir);
                builder.append('/');
            }
            index = next+1;
        }

        if (builder.length()>1 && builder.charAt(builder.length()-1)=='/')
            builder.deleteCharAt(builder.length()-1);
        return builder.toString();
    }

    public void pathBack(StringBuilder builder){
        builder.deleteCharAt(builder.length()-1);
        while (builder.length()>0 && builder.charAt(builder.length()-1)!='/')
            builder.deleteCharAt(builder.length()-1);
        if (builder.length()==0) builder.append('/');
    }
}