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import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.Arrays;
import java.util.ArrayList;
public class day09 {
public static void main(String args[]) throws IOException {
RandomAccessFile input = new RandomAccessFile("input", "r");
System.out.println("Day 09 Part 1: " + part1(input));
input.seek(0);
System.out.println("Day 09 Part 2: " + part2(input));
input.close();
}
public static String part1(RandomAccessFile input) throws IOException {
String line;
int sum = 0;
while ((line = input.readLine()) != null) {
String[] linea = line.split(" ");
int[] nums = new int[linea.length];
for (int i = 0; i < linea.length; i++) {
nums[i] = Integer.parseInt(linea[i]);
}
sum += predictNext(nums);
}
return Integer.toString(sum);
}
public static String part2(RandomAccessFile input) throws IOException {
String line;
int sum = 0;
while ((line = input.readLine()) != null) {
String[] linea = line.split(" ");
int[] nums = new int[linea.length];
for (int i = 0; i < linea.length; i++) {
nums[i] = Integer.parseInt(linea[i]);
}
sum += predictPre(nums);
}
return Integer.toString(sum);
}
private static int predictNext(int[] line) {
ArrayList<ArrayList<Integer>> differences = new ArrayList<>();
ArrayList<Integer> lastDiffs = new ArrayList<>();
for (int i: line) {
lastDiffs.add(i);
}
differences.add(lastDiffs);
while (!allZero(lastDiffs)) {
lastDiffs = getDifferences(lastDiffs);
differences.add(lastDiffs);
}
for (int i = differences.size() - 2; i >= 0; i--) {
ArrayList<Integer> lastrow = differences.get(i+1);
ArrayList<Integer> row = differences.get(i);
row.add(row.get(row.size() - 1) + lastrow.get(lastrow.size() - 1));
}
ArrayList<Integer> first = differences.get(0);
return first.get(first.size() - 1);
}
private static int predictPre(int[] line) {
ArrayList<ArrayList<Integer>> differences = new ArrayList<>();
ArrayList<Integer> lastDiffs = new ArrayList<>();
for (int i: line) {
lastDiffs.add(i);
}
differences.add(lastDiffs);
while (!allZero(lastDiffs)) {
lastDiffs = getDifferences(lastDiffs);
differences.add(lastDiffs);
}
int temp = 0;
for (int i = differences.size() - 2; i >= 0; i--) {
ArrayList<Integer> row = differences.get(i);
temp = row.get(0) - temp;
}
return temp;
}
private static boolean allZero(ArrayList<Integer> list) {
for(int i: list) {
if (i != 0) {
return false;
}
}
return true;
}
private static ArrayList<Integer> getDifferences(ArrayList<Integer> last) {
ArrayList<Integer> next = new ArrayList<>();
for (int i = 1; i < last.size(); i++) {
next.add(last.get(i) - last.get(i-1));
}
return next;
}
}
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