CareerCup

Looking for interview experience sharing and coaching?

Visit AONECODE.COM for ONE-ON-ONE private lessons by FB, Google and Uber engineers!

SYSTEM DESIGN
ALGORITHMS (conquer DP, Greedy, Graph, Advanced Algorithms, Clean Coding),
latest interview questions sorted by companies,
mock interviews.

Get hired from G, U, FB, Amazon, LinkedIn, Yahoo and other top-tier companies after weeks of training.

Email us aonecoding@gmail.com with any questions. Thanks!

import java.util.Stack;
class CharNode {
    char ch;
    CharNode prev;
    CharNode next;

    public CharNode(char ch) { this.ch = ch; }
}

class Edit {
    String edition; //"DEL", "INS", "LEFT", "RIGHT"
    CharNode data;
    public Edit(String edition, CharNode cur) {
        data = cur;
        this.edition = edition;
    }
}

public class TextEditor {
    private Stack<Edit> undo_stack;
    private CharNode cursor;
    private CharNode end;

    public TextEditor() {
        undo_stack = new Stack();
        end = new CharNode('\0');
        cursor = end;
    }

    public void moveCursorLeft() {
        if(cursor.prev == null) return;
        cursor = cursor.prev;
        undo_stack.push(new Edit("RIGHT", null));
    }

    public void moveCursorRight() {
        if(cursor == end) return;
        cursor = cursor.next;
        undo_stack.push(new Edit("LEFT", null));
    }

    public void insertCharacter(char ch) {
        CharNode n = new CharNode(ch);
        insert(n);
        undo_stack.push(new Edit("DEL", null));
    }

    public void backspace() {
        if(cursor.prev == null) return;
        undo_stack.push(new Edit("INS", delete(cursor.prev)));
    }

    public void undo() {
        if(undo_stack.isEmpty()) return;
        Edit edit = undo_stack.pop();
        switch(edit.edition) {
            case "LEFT":
                cursor = cursor.prev; break;
            case "RIGHT":
                cursor = cursor.next; break;
            case "DEL":
                delete(cursor.prev); break;
            case "INS":
                insert(edit.data); break;
            default:
                return;
        }
    }

    public String toString() {
        StringBuilder text = new StringBuilder();
        CharNode n = end.prev;
        if(cursor == end) text.append('|');
        while(n != null) {
            text.insert(0, n.ch);
            if(cursor == n) text.insert(0, '|');
            n = n.prev;
        }
        return text.toString();
    }

    private void insert(CharNode node) {
        CharNode prev = cursor.prev;
        node.next = cursor;
        cursor.prev = node;
        if(prev != null) {
            prev.next = node;
            node.prev = prev;
        }
    }

    private CharNode delete(CharNode del) {
        if(del.prev != null) {
            del.prev.next = cursor;
        }
        cursor.prev = del.prev;
        return del;
    }
}

Original Link: https://github.com/tabvn/ued/blob/master/careercup/google/design_text_editor.cpp

#include <iostream>
#include <vector>
#include <string>

const char CURSOR = '|';

struct Revision
{
	std::string text;
	int cursorIndex;

	Revision(){
		this->text = CURSOR;
		this->cursorIndex = 0;
	}

};


struct TextEditor
{

	std::vector<Revision> revisions; // store all revisions for undo
	int currentRevision;

	TextEditor(){

		this->currentRevision = 0;
		Revision r;

		this->revisions.push_back(r); 

		this->displayText("Start with empty text");
		
	}

	void displayText(std::string funcName){

		Revision revision = this->revisions[this->currentRevision];
		std::cout << funcName << std::endl;
		std::cout << "text = \"" << revision.text << "\"" << std::endl;
	}
	/*
	* Move cursor index to left
	*/
	void moveCursorLeft(){

		Revision r = this->revisions[this->currentRevision];
		char leftChar;

		if(r.cursorIndex > 0){
			leftChar = r.text[r.cursorIndex-1];
			r.text[r.cursorIndex-1] = CURSOR;
			r.text[r.cursorIndex] = leftChar;
			r.cursorIndex --;

			this->revisions.push_back(r);
			this->currentRevision ++;


		}

		this->displayText("moveCursorLeft()");




	}

	/*
	* Move cursor index to right
	*/
	void moveCursorRight(){

		Revision r = this->revisions[this->currentRevision];
		char rightChar;

		if(r.cursorIndex < r.text.size() -1){

			rightChar = r.text[r.cursorIndex+1];
			r.text[r.cursorIndex+1] = CURSOR;
			r.text[r.cursorIndex] = rightChar;
			r.cursorIndex ++;

			this->revisions.push_back(r);
			this->currentRevision ++;
		}

		this->displayText("moveCursorRight()");

	}

	/*
	* Insert the char right before cursor
	*/

	void insertCharacter(char ch){

		Revision r = this->revisions[this->currentRevision];
		r.text[r.cursorIndex] = ch;
		r.text += "|";
		r.cursorIndex++;

		this->revisions.push_back(r); // new revision become current revision
		this->currentRevision ++;

		std::string s = "insertCharacter('";
		s+= ch;
		s+= "')";
		this->displayText(s);
	}

	/*
	* delete the char right before cursor
	*/
	void backspace(){

		Revision r = this->revisions[this->currentRevision];
		if(r.text.size() > 1 && r.cursorIndex > 0){
				r.text.erase(r.cursorIndex - 1, 1);		
				r.cursorIndex --;

				this->revisions.push_back(r);
				this->currentRevision++;
		}

		this->displayText("backspace()");


	}

	/*
	* Undo last edit
	*/

	void undo(){

		if(this->currentRevision > 0){
			this->currentRevision--;
		}

		this->displayText("undo()");
	}
	
};



void beginTest(){

	TextEditor editor;

	editor.insertCharacter('a');
	editor.insertCharacter('b');
	editor.insertCharacter('c');

	editor.moveCursorLeft();
	editor.moveCursorLeft();
	editor.moveCursorLeft();

	editor.backspace();
	editor.moveCursorLeft();

	editor.undo();
	editor.undo();
	editor.undo();
	editor.undo();
	editor.undo();




}
int main(int argc, char const *argv[]){
	
	beginTest();

	return 0;
}

#include<list>
#include<stack>

using namespace std;

enum class _ops{ins, del};
struct UndoOps
{
    UndoOps(_ops ops, list<char>::const_iterator it, char ch=0)
    {
        this->ops=ops;
        this->it=it;
        this->ch=ch;
    }
    list<char>::const_iterator it;
    _ops ops;
    char ch;
};

class TextEditor
{
    private:
    stack<UndoOps> undo_stack;
    
    list<char> text;
    list<char>::const_iterator cur;

    public:
    TextEditor()
    {
        cur=text.end();
    }

    ~TextEditor()
    {
    }

    void left()
    {
        if(cur==text.begin()) return;
        --cur;
    }

    void right()
    {
        if(cur==text.end()) return;
        ++cur;
    }

    void ins(char ch)
    {
        cur=text.insert(cur, ch);
        undo_stack.push(UndoOps(_ops::del, cur));
        ++cur;
    }

    void backspace()
    {
        if(cur==text.begin()) return;
        list<char>::const_iterator item=cur;--item;
        char ch=*item;
        cur=item;cur--;
        text.erase(item);
        ++cur;
        undo_stack.push(UndoOps(_ops::ins, cur, ch));
    }

    void undo()
    {
        if(undo_stack.empty()) return;

        UndoOps undo=undo_stack.top();
        undo_stack.pop();

        switch(undo.ops)
        {
            case _ops::ins:
                cur=text.insert(undo.it, undo.ch);
                ++cur;
            break;
            case _ops::del:
            {
                cur=undo.it;--cur;
                text.erase(undo.it);
                ++cur;
            }
            break;
        }
    }

    void print()
    {
        for(list<char>::const_iterator it=text.begin();it!=text.end();it++)
        {
            if(cur==it)
                cout<<'|';
            cout<<*it;
        }
        if(cur==text.end())
            cout<<'|';
        cout<<endl;
    }
};

int main() {
    TextEditor editor;

    editor.ins('a'); editor.print();
    editor.ins('b'); editor.print();
    editor.ins('c'); editor.print();

    editor.left(); editor.print();
    editor.left(); editor.print();
    editor.left(); editor.print();

    editor.right(); editor.print();
    editor.right(); editor.print();
    editor.right(); editor.print();

    editor.backspace(); editor.print();
    editor.left(); editor.print();

    editor.undo(); editor.print();
    editor.undo(); editor.print();
    editor.undo(); editor.print();
    editor.undo(); editor.print();
    editor.undo(); editor.print();

  return 0;
}

results:
a|
ab|
abc|
ab|c
a|bc
|abc
a|bc
ab|c
abc|
ab|
a|b
abc|
ab|
a|
|
|

All above code has corner case issues; here is simplest and fixed

package Java.Design.TextEditor;

import java.util.LinkedList;
import java.util.List;
import java.util.Stack;

/**
 * Author: Nitin Gupta(nitin.gupta@walmart.com)
 * Date: 11/04/19
 * Description: 
 */
public class SimpleTextEditor implements ITextEditor {

    private Stack<Revision> undoStack; //holds the last action
    private CharacterNode cursor; //holds the current cursor position
    private CharacterNode start; //to print
    int totalSize = 0;

    public SimpleTextEditor() {
        this.undoStack = new Stack<>();
        this.cursor = new CharacterNode('\0');
        start = null;
    }

    @Override
    public void moveLeft() {
        if (cursor.getPrev() == null) return;
        cursor = cursor.getPrev();
        undoStack.push(new Revision(Action.RIGHT, null));
    }

    @Override
    public void moveRight() {
        if (cursor.getNext() == null) return;
        cursor = cursor.getNext();
        undoStack.push(new Revision(Action.LEFT, null));
    }

    @Override
    public void backspace() {
        if (cursor.getPrev() == null) return; //No data to delete
        totalSize--;
        CharacterNode deleted = delete(cursor.getPrev());
        undoStack.push(new Revision(Action.INSERT, deleted));
        if (totalSize == 0)
            start = null;


    }

    private CharacterNode delete(CharacterNode toDelete) {

        if (toDelete != null) {

            CharacterNode prev = toDelete.getPrev();
            CharacterNode next = toDelete.getNext();

            if (prev != null) {
                prev.setNext(next);
            }

            if (next != null)
                next.setPrev(prev);

            if (toDelete.getPrev() == null && totalSize == 0)
                start = null;

            if (toDelete == start)
                start = next;
        }

        if (cursor.getPrev() == null && totalSize == 0)
            start = null;


        return toDelete;

    }

    @Override
    public void insert(char data) {


        CharacterNode node = new CharacterNode(data);

        CharacterNode prev = cursor.getPrev();

        node.setNext(cursor);
        cursor.setPrev(node);

        if (prev != null) {
            prev.setNext(node);
            node.setPrev(prev);

        } else
            start = node;

        if (totalSize == 0)
            start = node;


        undoStack.push(new Revision(Action.DELETE, node));
        totalSize++;

    }

    @Override
    public void undo() {

        if (undoStack.isEmpty()) return;

        Revision action = undoStack.pop();

        switch (action.getAction()) {
            case LEFT:
                if (cursor != null)
                    cursor = cursor.getNext();
                break;
            case RIGHT:
                if (cursor != null)
                    cursor = cursor.getPrev();
                break;
            case DELETE:
                if (cursor != null) {
                    if (cursor.getPrev() == null)
                        start = null;

                    delete(cursor.getPrev());
                }
                break;
            case INSERT:

                insert(action.getData().getValue());
                break;
        }

    }

    @Override
    public String print() {
        List<CharacterNode> currentText = new LinkedList<>();
        CharacterNode temp = start;
        while (temp != null) {

            if (temp == cursor)
                currentText.add(new CharacterNode('|'));
            if (temp.getValue() != '\0')
                currentText.add(temp);
            temp = temp.getNext();
        }
        return currentText.toString();
    }


    @Override
    public CharacterNode getCursor() {
        return cursor;
    }
}

Simple C++ implementation with STL list:

class TextEditor
{
public:
	TextEditor()
    {
        text.push_back('|');
        cursor = text.begin();
	}

	void insertCharacter(char c)
	{
		text.insert(cursor, c);
        undoStack.push("b");
	}

	void moveCursorLeft()
	{
		if (cursor != text.begin())
        {
			text.splice(std::prev(cursor), text, cursor);
            undoStack.push("r");
        }
	}

	void moveCursorRight()
	{
		if (cursor != std::prev(text.end()))
        {
			text.splice(std::next(cursor, 2), text, cursor);
            undoStack.push("l");
        }
	}

	void backspace()
    {
        if (cursor != text.begin())
        {
            char c = *std::prev(cursor);
            string s = "a";
            undoStack.push(s + c);
            text.erase(std::prev(cursor));
        }
    }
    
    void undo()
    {
        if (!undoStack.empty())
        {
            string s = undoStack.top();
            undoStack.pop();
            
            if (s[0] == 'b')
                backspace();
            else if (s[0] == 'r')
                moveCursorRight();
            else if (s[0] == 'l')
                moveCursorLeft();
            else if (s[0] == 'a')
                insertCharacter(s[1]);
            
            // this second pop is needed because also the undo write to stack :D
            undoStack.pop();
        }
    }
    
    void print()
    {
        for (auto it = text.begin(); it != text.end(); ++it)
            std::cout << *it;
        
        std::cout << endl;
    }

private:
	list<char> text;
	list<char>::iterator cursor;
    stack<string> undoStack;
};

int main() {
    TextEditor te;
    
    te.print();
    
    te.insertCharacter('c');
    te.insertCharacter('i');
    te.insertCharacter('a');
    te.insertCharacter('o');
    
    te.print();
    
    te.moveCursorLeft();
    te.moveCursorLeft();
    
    te.print();
    
    te.moveCursorRight();
    te.moveCursorRight();
    
    te.print();
    
    te.backspace();
    
    te.print();
    
    te.undo();
    te.print();
    te.undo();
    te.print();
}