16a.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <string.h>
   4 #include <stdint.h>
   5
   6 char *hex2bin[] =
   7         { ['0'] = "0000", ['1'] = "0001", ['2'] = "0010", ['3'] = "0011"
   8         , ['4'] = "0100", ['5'] = "0101", ['6'] = "0110", ['7'] = "0111"
   9         , ['8'] = "1000", ['9'] = "1001", ['A'] = "1010", ['B'] = "1011"
  10         , ['C'] = "1100", ['D'] = "1101", ['E'] = "1110", ['F'] = "1111"
  11         , ['\n'] = "0000"};
  12
  13 struct stream { int pos; char *buf; };
  14
  15 int next(struct stream *f)
  16 {
  17         if (*f->buf == '\0') {
  18                 int c = getchar();
  19                 if (c == EOF) {
  20                         printf("EOF\n");
  21                         exit(1);
  22                 }
  23                 f->buf = hex2bin[c];
  24         }
  25         int r =*(f->buf++) == '1' ? 1 : 0;
  26         f->pos++;
  27         return r;
  28 }
  29
  30 int bin2int(struct stream *f, int n)
  31 {
  32         int r = 0;
  33         for (int i = 0; i<n; i++)
  34                 r = 2*r+next(f);
  35         return r;
  36 }
  37
  38 int parse_packet(struct stream *f)
  39 {
  40         int packetversion = bin2int(f, 3);
  41         int packettype = bin2int(f, 3);
  42
  43         switch (packettype) {
  44         //Literal value
  45         case 4: {
  46                 int num = 0;
  47                 while (next(f) == 1) {
  48                         num = num*16+bin2int(f, 4);
  49                 }
  50                 num = num*16+bin2int(f, 4);
  51                 break;
  52         }
  53         default: {
  54                 int lengthtypeid = next(f);
  55
  56                 //length is 15
  57                 if (lengthtypeid == 0) {
  58                         int lengthsubpackets = bin2int(f, 15);
  59                         int oldpos = f->pos;
  60
  61                         while (f->pos - oldpos < lengthsubpackets)
  62                                 packetversion += parse_packet(f);
  63                 } else {
  64                         int numsubpackets = bin2int(f, 11);
  65                         for (int i = 0; i<numsubpackets; i++)
  66                                 packetversion += parse_packet(f);
  67                 }
  68                 break;
  69         }}
  70         return packetversion;
  71 }
  72
  73 int main()
  74 {
  75         struct stream f = {.pos=0, .buf=""};
  76         printf("r: %d\n", parse_packet(&f));
  77 }