File System - Amazon Top Interview Questions


Problem Statement :


Implement a data structure with the following methods:

bool create(String path, int content) which creates a path at path if there's a parent directory and path doesn't exist yet, and sets its value as content. Returns whether it was newly created. Initially only the root directory at "/" exists.
int get(String path) which returns the value associated with path. If there's no path, return -1.
Constraints

0 ≤ n ≤ 100,000 where n is the number of calls to create and get

Example 1

Input

methods = ["constructor", "create", "create", "get", "get", "create", "get"]
arguments = [[], ["/usr", 1], ["/usr/bin", 2], ["/usr"], ["/usr/bin"], ["/proc/1/exe", 3], ["/non/existent"]]`

Output

[None, True, True, 1, 2, False, -1]

Explanation

fs = FileSystem() # Only "/" exists
fs.create("/usr", 1) == True # Now "/" and "/usr" exists
fs.create("/usr/bin", 2) == True# Now "/", "/usr" and "/usr/bin" exists
fs.get("/usr") == 1
fs.get("/usr/bin") == 2
fs.create("/proc/1/exe", 3) == False # Parent dir "/proc/1/" doesn't exist, so can't create here
fs.get("/non/existent") == -1



Solution :



title-img




                        Solution in C++ :

struct Node {
    string folderName;
    int content;
    unordered_map<string, Node*> children;
    Node(string name, int c) {
        folderName = name;
        content = c;
        children.clear();
    }
};

class FileSystem {
    private:
    Node* root;
    vector<string> getFolders(string path) {
        path = path.substr(1);
        vector<string> folders;
        string temp = "";

        for (int i = 0; i < path.size(); i++) {
            if (path[i] != '/') {
                temp.push_back(path[i]);
            } else {
                folders.push_back(temp);
                temp = "";
            }
        }
        if (temp != "") folders.push_back(temp);
        return folders;
    }

    bool createHelper(string path, int content) {
        vector<string> folders = getFolders(path);
        bool newlyCreated = false;

        // cout<<"CREATE"<<endl;
        // for(auto x: folders)
        //     cout<<x<<" ";
        // cout<<endl;

        int ptr = 0;
        Node* currentNode = root;
        while (ptr < folders.size()) {
            if (currentNode->children.find(folders[ptr]) != currentNode->children.end()) {
                // cout<<"ALREADY HERE "<<folders[ptr]<<endl;
                currentNode = currentNode->children[folders[ptr]];
            } else {
                // cout<<"NEW HERE "<<folders[ptr]<<endl;
                if (ptr != folders.size() - 1) return false;
                newlyCreated = true;
                Node* node = new Node(folders[ptr], content);
                currentNode->children[folders[ptr]] = node;
                currentNode = node;
            }
            ptr++;
        }
        // cout<<endl<<endl;
        return newlyCreated;
    }
    int getHelper(string path) {
        vector<string> folders = getFolders(path);
        Node* currentNode = root;

        int ptr = 0;
        while (ptr < folders.size()) {
            if (currentNode->children.find(folders[ptr]) == currentNode->children.end()) return -1;
            currentNode = currentNode->children[folders[ptr]];
            ptr++;
        }
        return currentNode->content;
    }

    public:
    FileSystem() {
        root = new Node(".root", -1);
    }

    int get(string path) {
        return getHelper(path);
    }

    bool create(string path, int content) {
        return createHelper(path, content);
    }
};
                    




                        Solution in Python : 
                            
class FileTree:
    def __init__(self):
        self.children = {}
        self.value = None


class FileSystem:
    def __init__(self):
        self.tree = FileTree()
        self.tree.children[""] = FileTree()

    def insert(self, pathList, content):
        temp = self.tree
        for idx, path in enumerate(pathList):
            if path not in temp.children:
                if idx < len(pathList) - 1:
                    return False
                temp.children[path] = FileTree()
            temp = temp.children[path]
        if temp.value != None:
            return False
        temp.value = content
        return True

    def get(self, path):
        temp = self.tree
        for path in path.split("/"):
            if path not in temp.children:
                return -1
            temp = temp.children[path]
        return temp.value if temp.value != None else -1

    def create(self, path, content):
        return True if self.insert(path.split("/"), content) else False
                    


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