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Task/Percolation-Mean-cluster-density/C/percolation-mean-cluster-density.c

@@ -0,0 +1,77 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int *map, w, ww;
+
+void make_map(double p)
+{
+	int i, thresh = RAND_MAX * p;
+	i = ww = w * w;
+
+	map = realloc(map, i * sizeof(int));
+	while (i--) map[i] = -(rand() < thresh);
+}
+
+char alpha[] = "+.ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+		"abcdefghijklmnopqrstuvwxyz";
+#define ALEN ((int)(sizeof(alpha) - 3))
+
+void show_cluster(void)
+{
+	int i, j, *s = map;
+
+	for (i = 0; i < w; i++) {
+		for (j = 0; j < w; j++, s++)
+			printf(" %c", *s < ALEN ? alpha[1 + *s] : '?');
+		putchar('\n');
+	}
+}
+
+void recur(int x, int v) {
+	if (x >= 0 && x < ww && map[x] == -1) {
+		map[x] = v;
+		recur(x - w, v);
+		recur(x - 1, v);
+		recur(x + 1, v);
+		recur(x + w, v);
+	}
+}
+
+int count_clusters(void)
+{
+	int i, cls;
+
+	for (cls = i = 0; i < ww; i++) {
+		if (-1 != map[i]) continue;
+		recur(i, ++cls);
+	}
+
+	return cls;
+}
+
+double tests(int n, double p)
+{
+	int i;
+	double k;
+
+	for (k = i = 0; i < n; i++) {
+		make_map(p);
+		k += (double)count_clusters() / ww;
+	}
+	return k / n;
+}
+
+int main(void)
+{
+	w = 15;
+	make_map(.5);
+	printf("width=15, p=0.5, %d clusters:\n", count_clusters());
+	show_cluster();
+
+	printf("\np=0.5, iter=5:\n");
+	for (w = 1<<2; w <= 1<<14; w<<=2)
+		printf("%5d %9.6f\n", w, tests(5, .5));
+
+	free(map);
+	return 0;
+}