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 :
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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