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  1. #include <stdlib.h>
  2. #include <stdio.h>
  3.  
  4. #define MAXK 1000006
  5.  
  6. static int K;
  7.  
  8. static struct STATE{
  9.     int len;
  10.     char letter;
  11.     STATE *prev[20];
  12. } *state[MAXK];
  13.  
  14. void Init() {}
  15.  
  16. STATE *make(int len, char letter, STATE *prev)
  17. {
  18.     STATE *ret=(STATE*)malloc(sizeof(STATE));
  19.     ret->len = len; ret->letter = letter;
  20.     for (int i=0;i<20;i++) ret->prev[i] = NULL;
  21.     ret->prev[0] = prev;
  22.     for (int i=0;i<19&&ret->prev[i];i++){
  23.         ret->prev[i+1] = ret->prev[i]->prev[i];
  24.     }
  25.     return ret;
  26. }
  27.  
  28. void TypeLetter(char letter)
  29. {
  30.     STATE *tmp;
  31.     if (state[K]) tmp = make(state[K]->len+1,letter,state[K]);
  32.     else tmp = make(1,letter,NULL);
  33.     state[++K] = tmp;
  34. }
  35.  
  36. void UndoCommands(int steps)
  37. {
  38.     state[++K] = state[K-steps-1];
  39. }
  40.  
  41. char GetLetter(int pos)
  42. {
  43.     STATE *now=state[K];
  44.     int bef=now->len-pos-1,i;
  45.     for (i=20;i--;) if ((bef>>i)&1){
  46.         now = now->prev[i];
  47.     }
  48.     return now->letter;
  49. }
  50.  
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https://ideone.com/krpgVl
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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