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#include <stdio.h>
#define COLUMNS 8
#define ROWS 128
int seat_id(const char *seat)
{
int row = 0;
int row_lower = 0;
int row_upper = ROWS - 1;
int column = 0;
int column_lower = 0;
int column_upper = COLUMNS - 1;
int i = 0;
for (; i < 6; i++) {
switch (seat[i]) {
case 'F':
row_upper -= (row_upper - row_lower + 1) / 2;
break;
case 'B':
row_lower += (row_upper - row_lower + 1) / 2;
break;
}
}
switch (seat[i++]) {
case 'F':
row = row_lower;
break;
case 'B':
row = row_upper;
break;
}
for (; i < 9; i++) {
switch (seat[i]) {
case 'L':
column_upper -= (column_upper - column_lower + 1) / 2;
break;
case 'R':
column_lower += (column_upper - column_lower + 1) / 2;
break;
}
}
switch (seat[i++]) {
case 'L':
column = column_lower;
break;
case 'R':
column = column_upper;
break;
}
return row * COLUMNS + column;
}
int missing_seat_id(const char *filename)
{
FILE *file = fopen(filename, "r");
char table[COLUMNS * ROWS] = { 0 };
// Include space for newline and string terminator
char buffer[16] = { 0 };
int min = __INT_MAX__;
int max = 0;
while (fgets(buffer, 16, file)) {
int tmp = seat_id(buffer);
if (tmp > max)
{
max = tmp;
}
if (tmp < min)
{
min = tmp;
}
table[tmp] = 1;
}
for (int i = min + 1; i < max; i++) {
if (table[i] == 0) {
return i;
}
}
return 0;
}
int main(int argc, char *argv[])
{
printf("%i", missing_seat_id(argv[argc - 1]));
}
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