[leetcode]Simplify Path

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.

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".

算法思路：

栈。设置两指针，根据‘/’分割出一个一个的路径名，压栈。pop的时候，遇到‘.’和“”（//生产的）不用管，".."回滚，并记录回滚次数。

注意：当路径为空时，要返回 / 。

吐槽：有一个奇葩case -> /... 后来才反映过来，人家的路径名叫...搞笑吗？

 1 public class Solution {
 2     public String simplifyPath(String path) {
 3         if(path == null || path.length() == 0) return "";
 4         int start = 0;
 5         Stack<String> stack = new Stack<String>();
 6         for(int i = 1; i < path.length(); i++){
 7             if(path.charAt(i) == '/' || i == path.length() - 1){
 8                    String s = (path.charAt(i) == '/') ? path.substring(start + 1, i) : path.substring(start + 1, i + 1);
 9                    stack.push(s);
10                    start = i;
11             }
12         }
13         StringBuilder sb = new StringBuilder();
14         int traceBack = 0;
15         while(!stack.isEmpty()){
16             String str = stack.pop();
17             if(".".equals(str) || str.length() == 0)continue;
18             else if("..".equals(str)) {
19                 traceBack++;
20             }else{
21                 traceBack--;
22                 if(traceBack < 0){
23                     sb.insert(0,  "/" + str);
24                     traceBack = 0;
25                 }
26             }
27         }
28         return sb.toString().length() == 0 ? "/" : sb.toString();
29     }
30 }

第二遍：直接在扫描的时候就进行压栈、弹栈处理

代码如下：

public class Solution {
    public String simplifyPath(String path) {
        if(path == null || path.length() == 0) return "/";
        int length = path.length();
        Stack<String> stack = new Stack<String>();
        int i = 0;
        while(i < length){
            if(path.charAt(i) == '/'){
                int begin = i;
                do{
                    i++;
                }while(i < length && path.charAt(i) != '/');
                String tem = path.substring(begin + 1,i);
                if("".equals(tem) || ".".equals(tem)) continue;
                else if("..".equals(tem)){
                    if(!stack.isEmpty())
                        stack.pop();
                }else{
                    stack.push(tem);
                }
            }
        }
        StringBuilder sb = new StringBuilder();
        while(!stack.isEmpty()){
            sb.insert(0,stack.pop()).insert(0,"/");
        }
        return sb.toString().length() == 0 ? "/" : sb.toString();
    }
}