87 lines
2.3 KiB
C
87 lines
2.3 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#define SERIAL 7347
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#define DIMENSIONS 300
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int initialFieldValue(int x, int y) {
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int id = x + 10;
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int power = id * y + SERIAL;
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power *= id;
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char itoa [10];
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int len = sprintf(itoa, "%d", power);
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if (len < 3) {
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return 0;
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}
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// manually set a nullbyte after the hundreds digit
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itoa[len-2] = 0;
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int parsed = (int) strtol(&itoa[len-3], NULL, 10);
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return parsed - 5;
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}
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void setFields(int fields[DIMENSIONS][DIMENSIONS]) {
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for (int i=0; i<DIMENSIONS; i++) {
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for (int j=0; j<DIMENSIONS; j++) {
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fields[i][j] = initialFieldValue(i+1, j+1);
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}
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}
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}
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// https://en.wikipedia.org/wiki/Summed-area_table
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void setSummedArea(int sums[DIMENSIONS][DIMENSIONS], int input[DIMENSIONS][DIMENSIONS]) {
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sums[0][0] = input[0][0];
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// Topmost row
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for (int x=1; x<DIMENSIONS; x++) {
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int y = 0;
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sums[x][y] = input[x][y] + sums[x-1][y];
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}
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// Leftmost column
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for (int y=1; y<DIMENSIONS; y++) {
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int x = 0;
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sums[x][y] = input[x][y] + sums[x][y-1];
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}
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for (int x=1; x<DIMENSIONS; x++) {
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for (int y=1; y<DIMENSIONS; y++) {
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sums[x][y] = input[x][y] + sums[x][y-1] + sums[x-1][y] - sums[x-1][y-1];
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}
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}
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}
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int max(int a, int b) {
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return a > b ? a : b;
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}
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int calculateNeighborhood(int fields[DIMENSIONS][DIMENSIONS], int x, int y, int size) {
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return fields[x-1][y-1] + fields[x+size][y+size] - fields[x-1][y+size] - fields[x+size][y-1];
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}
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int main() {
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int fields[DIMENSIONS][DIMENSIONS];
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setFields(fields);
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int summedAreaFields[DIMENSIONS][DIMENSIONS];
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setSummedArea(summedAreaFields, fields);
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// Part 1
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int maxPower = -999999999;
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int maxX, maxY;
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int maxSize = 0;
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for (int x=1; x<DIMENSIONS-3; x++) {
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for (int y=1; y<DIMENSIONS-3; y++) {
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for (int size=3; size<DIMENSIONS-max(x, y); size++) {
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int moore = calculateNeighborhood(summedAreaFields, x, y, size);
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if (moore > maxPower) {
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maxPower = moore;
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maxX = x + 1;
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maxY = y + 1;
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maxSize = size + 1;
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}
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}
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}
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}
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printf("x: %d, y: %d, size: %d, power: %d\n", maxX, maxY, maxSize, maxPower);
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return 0;
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}
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