UVa 11660 - Look-and-Say sequences

Accepted date: 2015-09-15
Ranking (as of 2015-09-15): 1 out of 275
Language: C++

/*
  UVa 11660 - Look-and-Say sequences

  To build using Visual Studio 2012:
    cl -EHsc -O2 UVa_11660_Look_and_Say_sequences.cpp
*/

#include <algorithm>
#include <cstdio>
using namespace std;

const int i_max = 1000;

void look_and_say_sequence(const char* s, char* t)
{
  int ctr = 1;
  char d = *s++;
  char* u = t;
  for ( ; *s; s++) {
    if (*s != d) {
      *t++ = ctr + '0';
      *t++ = d;
      if (t - u >= i_max) {
        *t = '\0';
        return;
      }
      ctr = 1;
      d = *s;
    }
    else
      ctr++;
  }
  *t++ = ctr + '0';
  *t++ = d;
  *t = '\0';
}

int main()
{
  while (true) {
    int i, j;
    char s[i_max + 1], t[i_max + 1];
    scanf("%s %d %d", s, &i, &j);
    if (s[0] == '0' && !i && !j)
      break;
    char *p = s, *q = t;
    for (int k = 1; k < i; k++) {
      look_and_say_sequence(p, q);
      swap(p, q);
#ifdef DEBUG
      printf("%s\n", p);
#endif
    }
    printf("%c\n", *(p + j - 1));
  }
  return 0;
}