2021/day09.c


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#include <stdio.h>
#include <stdlib.h>
static int h, w;
static int grid[128][128];
static int adj(int *a, int y, int x) {
	int n = 0;
	if (y > 0) a[n++] = grid[y-1][x];
	if (y < h-1) a[n++] = grid[y+1][x];
	if (x > 0) a[n++] = grid[y][x-1];
	if (x < w-1) a[n++] = grid[y][x+1];
	return n;
}
int main(void) {
	size_t cap = 0;
	char *buf = NULL;
	while (0 < getline(&buf, &cap, stdin)) {
		for (w = 0; buf[w] && buf[w] != '\n'; ++w) {
			grid[h][w] = buf[w] - '0';
		}
		h++;
	}
	int risk = 0;
	for (int y = 0; y < h; ++y)
	for (int x = 0; x < w; ++x) {
		int a[4];
		int n = adj(a, y, x);
		int m = 0;
		for (int i = 0; i < n; ++i) {
			if (a[i] <= grid[y][x]) m |= 1;
		}
		if (!m) risk += 1 + grid[y][x];
	}
	printf("%d\n", risk);
}