【字符串】Simplify Path（栈）

/**
 * @param {string} path
 * @return {string}
 */
var simplifyPath = function(path) {
    var stack=[],len=path.length,i=0;
    while(i<len){
        //跳过开头的‘/‘‘
        while(path[i]==‘/‘&&i<len){
            i++;
        }
        
        var s=‘‘;
        while(i<len&&path[i]!=‘/‘){
            s+=path[i++];
        }
        
        //如果是".."则需要弹栈，否则入栈
        if(".." == s && stack.length!=0){
            stack.pop();
        }else if(s != "" && s != "." && s != ".."){
            stack.push(s);
        }
            
    }
    
    //如果栈为空，说明为根目录，只有斜线‘/‘
    if(stack.length==0){
        return ‘/‘
    }
    var res=‘‘;
    while(stack.length!=0){
        res = "/" + stack.pop() + res;
    }         
    return res;
};