/*
Solution for Scrivener, with TypeLetter and GetLetter in O(log N) and UndoCommands in O(1).
Author: Matteo Boscariol
*/
#include<cstdlib>
#define MAXC 1000000
#define LOGMAXC 20
class node {
public:
char l;
node** parents;
int depth;
node(char letter, node* parent) {
l = letter;
if(parent == NULL) {
depth=-1;
parents = new node*[1];
parents[0] = NULL;
}
else {
depth=parent->depth+1;
parents = new node*[LOGMAXC];
parents[0] = parent;
for(int i=1, j=2; j<=depth+1; i++, j*=2) {
parents[i] = parents[i-1]->parents[i-1];
}
}
};
};
node** command_base;
int n_commands;
node* current_position;
node* tree_root;
void Init() {
command_base = new node*[MAXC];
n_commands = 0;
current_position = tree_root = new node('\0',NULL);
}
void TypeLetter(char L) {
command_base[n_commands] = current_position;
n_commands++;
node* n = new node(L, current_position);
current_position = n;
}
void UndoCommands(int U) {
node *n = command_base[n_commands - U];
command_base[n_commands] = current_position;
n_commands++;
current_position = n;
}
char GetLetter(int P) {
node* n = current_position;
int distance = current_position->depth - P;
for(int shift = LOGMAXC; shift >= 0; shift--) {
if((distance >> shift)%2 == 1)
n = n->parents[shift];
}
return n->l;
}
