111 lines
2.5 KiB
C
111 lines
2.5 KiB
C
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#include <stdlib.h>
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#include <stdio.h>
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#include <stdbool.h>
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#define LINES 1000
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// power! x to the y!
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int pow(int x, int y)
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{
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int ans = 1;
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for (int i = 0; i < y; i++) ans *= x;
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return ans;
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}
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// parse string into array of numbers
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int parse_numbers(char *str_row, int *row, int n)
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{
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int i = 0;
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for (; str_row[i] != '\n'; i++);
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for (; i >= 0; i--) {
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int pos = 0;
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for (; str_row[i] >= '0' && str_row[i] <= '9' && i >= 0; i--) {
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row[n] += (str_row[i] - '0') * pow(10, pos);
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pos++;
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}
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n--;
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}
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return 1;
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}
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// check if specific report is safe
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int check_report(int *row, int len)
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{
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// read number. Compare next number (higher, lower, +-1-2)
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// if you get to row[i + 1]line, ++
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bool rising = 0;
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bool first = 1;
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for (int i = 0; i < len - 1; i++) {
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// if difference isnt 1-3
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if (abs(row[i + 1] - row[i]) > 3 || abs(row[i + 1] - row[i]) < 1)
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return 0;
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// only for first comparison of row. Set direction.
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if (first && ((row[i + 1] - row[i]) < 0))
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rising = 0;
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else if (first)
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rising = 1;
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// for other comparisons, compare current direction to the previous.
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if (!first && (rising != !((row[i + 1] - row[i]) < 0))) {
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// printf("rising: %d while %d - %d is %d\n", rising, row[i + 1], row[i], row[i + 1] - row[i]);
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return 0;
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}
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// get ready for the next comparisons!
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first = 0;
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}
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return 1;
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}
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int dampener(int *row, int len)
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{
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if (check_report(row, len))
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return 1;
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for (int i = 0; i < len; i++) {
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int *dampened_row = malloc((len - 1) * sizeof(int));
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// initialize shorter array, but skip element i
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bool skipped = 0;
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for (int j = 0; j < len - 1; j++) {
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if (j != i && !skipped) {
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dampened_row[j] = row[j];
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}
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else {
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dampened_row[j] = row[j + 1];
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skipped = 1;
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}
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}
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if (check_report(dampened_row, len - 1)) {
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free(dampened_row);
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return 1;
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}
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free(dampened_row);
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}
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return 0;
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}
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int main()
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{
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int safe = 0;
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// read input row into array, count elements
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FILE *input;
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input = fopen("./input", "r");
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char line[32];
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for (int i = 0; i < LINES; i++) {
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// get string (line), count numbers, put into int array (row)
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int numbers = 1;
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fgets(line, sizeof(line), input);
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// count number of numbers, allocate memory
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for (int c = 0; line[c]; c++) numbers += (line[c] == ' ');
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int *row = (int *)calloc(numbers, sizeof(int));
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// parse numbers into array
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parse_numbers(line, row, numbers);
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// for (int j = 0; j < numbers; j++) printf("%d ", row[j]);
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// printf("\n\n");
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// send elements and length to check_report, add result to sum
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safe += dampener(row, numbers);
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free(row);
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}
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printf("%d\n", safe);
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}
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