Data commit

Task/Percolation-Bond-percolation/C/percolation-bond-percolation.c

@@ -0,0 +1,100 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// cell states
+#define FILL 1
+#define RWALL 2 // right wall
+#define BWALL 4 // bottom wall
+
+typedef unsigned int c_t;
+
+c_t *cells, *start, *end;
+int m, n;
+
+void make_grid(double p, int x, int y)
+{
+    int i, j, thresh = RAND_MAX * p;
+    m = x, n = y;
+
+    // Allocate two addition rows to avoid checking bounds.
+    // Bottom row is also required by drippage
+    start = realloc(start, m * (n + 2) * sizeof(c_t));
+    cells = start + m;
+
+    for (i = 0; i < m; i++)
+        start[i] = BWALL | RWALL;
+
+    for (i = 0, end = cells; i < y; i++) {
+        for (j = x; --j; )
+            *end++ = (rand() < thresh ? BWALL : 0)
+                |(rand() < thresh ? RWALL : 0);
+        *end++ = RWALL | (rand() < thresh ? BWALL: 0);
+    }
+    memset(end, 0, sizeof(c_t) * m);
+}
+
+void show_grid(void)
+{
+    int i, j;
+
+    for (j = 0; j < m; j++) printf("+--");
+    puts("+");
+
+    for (i = 0; i <= n; i++) {
+        putchar(i == n ? ' ' : '|');
+        for (j = 0; j < m; j++) {
+            printf((cells[i*m + j] & FILL) ? "[]" : "  ");
+            putchar((cells[i*m + j] & RWALL) ? '|' : ' ');
+        }
+        putchar('\n');
+
+        if (i == n) return;
+
+        for (j = 0; j < m; j++)
+            printf((cells[i*m + j] & BWALL) ? "+--" : "+  ");
+        puts("+");
+    }
+}
+
+int fill(c_t *p)
+{
+    if ((*p & FILL)) return 0;
+    *p |= FILL;
+    if (p >= end) return 1; // success: reached bottom row
+
+    return  ( !(p[ 0] & BWALL) && fill(p + m) ) ||
+        ( !(p[ 0] & RWALL) && fill(p + 1) ) ||
+        ( !(p[-1] & RWALL) && fill(p - 1) ) ||
+        ( !(p[-m] & BWALL) && fill(p - m) );
+}
+
+int percolate(void)
+{
+    int i;
+    for (i = 0; i < m && !fill(cells + i); i++);
+
+    return i < m;
+}
+
+int main(void)
+{
+    make_grid(.5, 10, 10);
+    percolate();
+    show_grid();
+
+    int cnt, i, p;
+
+    puts("\nrunning 10x10 grids 10000 times for each p:");
+    for (p = 1; p < 10; p++) {
+        for (cnt = i = 0; i < 10000; i++) {
+            make_grid(p / 10., 10, 10);
+            cnt += percolate();
+            //show_grid(); // don't
+        }
+        printf("p = %3g: %.4f\n", p / 10., (double)cnt / i);
+    }
+
+    free(start);
+    return 0;
+}