71. Simplify Path（js）

71. Simplify Path

Given an absolute path for a file (Unix-style), simplify it. Or in other words, convert it to the canonical path.

In a UNIX-style file system, a period . refers to the current directory. Furthermore, a double period .. moves the directory up a level. For more information, see: Absolute path vs relative path in Linux/Unix

Note that the returned canonical path must always begin with a slash /, and there must be only a single slash / between two directory names. The last directory name (if it exists) must not end with a trailing /. Also, the canonical path must be the shortest string representing the absolute path.

Example 1:

Input: "/home/"
Output: "/home"
Explanation: Note that there is no trailing slash after the last directory name.

Example 2:

Input: "/../"
Output: "/"
Explanation: Going one level up from the root directory is a no-op, as the root level is the highest level you can go.

Example 3:

Input: "/home//foo/"
Output: "/home/foo"
Explanation: In the canonical path, multiple consecutive slashes are replaced by a single one.

Example 4:

Input: "/a/./b/../../c/"
Output: "/c"

Example 5:

Input: "/a/../../b/../c//.//"
Output: "/c"

Example 6:

Input: "/a//b////c/d//././/.."
Output: "/a/b/c"
题意：unix系统的路径简化

/**
 * @param {string} path
 * @return {string}
 */
var simplifyPath = function(path) {
//     法一
    // let v=[];
    // let i=0;
    // while(i<path.length){
    //     while(path[i]==='/' && i<path.length) i++;
    //     if(i===path.length) break;
    //     let start=i;
    //     while(path[i]!=='/' && i<path.length) i++;
    //     let end=i-1;
    //     let s=path.substr(start,end-start+1);
    //     if(s==='..'){
    //         if(v.length>0) v.pop();
    //     }else if(s!=='.'){
    //         v.push(s);
    //     }
    // }
    // if(v.length===0) return '/';
    // let res='';
    // for(let i=0;i<v.length;i++){
    //     res+='/'+v[i];
    // }
    // return res;
//     法二
    return '/'+path.split('/').filter(str=> str!=='' && str!=='.').reduce((arr,str)=>{
        if(str==='..') arr.pop();
        else arr.push(str);
        return arr;
    },[]).join('/');
};