https://www.hackerrank.com/challenges/simple-text-editor
https://www.hackerrank.com/rest/contests/master/challenges/simple-text-editor/hackers/antrromet/download_solution
In this problem, your task is to implement a simple text editor. Initially, a file contains an empty string . Your task is to perform operations consisting of the following types:
- append - Appends the string at the end of .
- erase - Erase the last character of .
- get - Returns the character of .
- undo - Undo the last not previously undone operation of type or , so it reverts to the state before that operation.
For each operation of type , print a single line with the returned character of that operation.
Sample Input
9
1 abc
3 3
2 3
1 xy
3 2
4
4
3 1
Sample Output
c
y
a Scanner sc = new Scanner(System.in);
int Q = sc.nextInt();
sc.nextLine();
StringBuilder s = new StringBuilder();
Stack<String> stack = new Stack<String>();
for(int i=0;i<Q;i++){
String line = sc.nextLine();
String[] split = line.split(" ");
int t = Integer.valueOf(split[0]);
switch(t){
case 1:
String w = split[1];
s.append(w);
stack.push(1+" "+w.length());
break;
case 2:
int k = Integer.valueOf(split[1]);
stack.push(2+" "+s.substring(s.length() - k));
s.setLength(s.length() - k);
break;
case 3:
k = Integer.valueOf(split[1]);
System.out.println(s.charAt(k-1));
break;
case 4:
String undo = stack.pop();
String undoItems[] = undo.split(" ");
if(undoItems[0].equals("1")){
s.setLength(s.length() - Integer.valueOf(undoItems[1]));
} else {
s.append(undoItems[1]);
}
break;
}
}
https://www.hackerrank.com/rest/contests/master/challenges/simple-text-editor/hackers/akshaynayak/download_solution Scanner sc=new Scanner(System.in);
int n=sc.nextInt();
Stack<String> st=new Stack<String>();
st.push("");
int k=-1;
String prev="";
for(int i=0;i<n;i++){
int op=sc.nextInt();
switch(op){
case 1:
String newstr=sc.next();
prev=st.peek();
st.push(prev+newstr);
break;
case 2:
k=sc.nextInt();
prev=st.peek();
String temp=prev.substring(0,prev.length()-k);
st.push(temp);
break;
case 3:
k=sc.nextInt();
System.out.println(st.peek().charAt(k-1));
break;
case 4:
st.pop();
break;
}
https://www.hackerrank.com/rest/contests/master/challenges/simple-text-editor/hackers/MarcGoVi/download_solution Scanner sc = new Scanner(System.in);
int q = sc.nextInt();
Stack<String> stack = new Stack<String>();
String s = "";
for (int x = 0; x < q; x++) {
int ope = sc.nextInt();
switch (ope) {
case 1: //append
stack.push(s);
String append = sc.next();
s += append;
break;
case 2: //erase last x characters
stack.push(s);
int character = sc.nextInt();
s = s.substring(0, s.length() - character);
break;
case 3: //print
int index = sc.nextInt();
System.out.println(s.charAt(index - 1));
break;
case 4: //undo
s = stack.pop();
break;
default:
break;
}
}
http://www.martinkysel.com/hackerrank-simple-text-editor-solution/
I maintain two separate stacks. Self.stack represents the current state of the text. I can read data from this stack by indexing it. Self.cmds keeps the history of commands. Each command type knows how to execute itself and how to revert itself.
class AppendCmd(): def execute(self, stack, value): self.length = len(value) stack.extend(value) def revert(self, stack): for _ in xrange(self.length): stack.pop()class EraseCmd(): def execute(self, stack, value): self.text = stack[-value:] for _ in xrange(value): stack.pop() def revert(self, stack): stack.extend(self.text) class CustomStack: def __init__(self): self.stack = [] self.cmds = [] def push(self, value): cmd = AppendCmd() cmd.execute(self.stack, value) self.cmds.append(cmd) def pop(self, value): cmd = EraseCmd() cmd.execute(self.stack, value) self.cmds.append(cmd) def get(self, value): print self.stack[value] def revert(self): cmd = self.cmds.pop() cmd.revert(self.stack)def main(): cs = CustomStack() N = int(raw_input()) for _ in xrange(N): unknown = raw_input() command = unknown[0] if command == '1': cmd, value = unknown.split() cs.push(list(value)) elif command == '2': cmd, value = map(int, unknown.split()) cs.pop(value) elif command == '3': cmd, value = map(int, unknown.split()) cs.get(value - 1) else: cs.revert()