tasks a-s

Task/Probabilistic-choice/C/probabilistic-choice-1.c

@@ -0,0 +1,34 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+/* pick a random index from 0 to n-1, according to probablities listed
+   in p[] which is assumed to have a sum of 1. The values in the probablity
+   list matters up to the point where the sum goes over 1 */
+int rand_idx(double *p, int n)
+{
+	double s = rand() / (RAND_MAX + 1.0);
+	int i;
+	for (i = 0; i < n - 1 && (s -= p[i]) >= 0; i++);
+	return i;
+}
+
+#define LEN 8
+#define N 1000000
+int main()
+{
+	const char *names[LEN] = { "aleph", "beth", "gimel", "daleth",
+			  "he", "waw", "zayin", "heth" };
+	double s, p[LEN] = { 1./5, 1./6, 1./7, 1./8, 1./9, 1./10, 1./11, 1e300 };
+	int i, count[LEN] = {0};
+
+	for (i = 0; i < N; i++) count[rand_idx(p, LEN)] ++;
+
+	printf("  Name  Count    Ratio Expected\n");
+	for (i = 0, s = 1; i < LEN; s -= p[i++])
+		printf("%6s%7d %7.4f%% %7.4f%%\n",
+			names[i], count[i],
+			(double)count[i] / N * 100,
+			((i < LEN - 1) ? p[i] : s) * 100);
+
+	return 0;
+}

Task/Probabilistic-choice/C/probabilistic-choice-2.c

@@ -0,0 +1,9 @@
+  Name  Count    Ratio Expected
+ aleph 199928 19.9928% 20.0000%
+  beth 166489 16.6489% 16.6667%
+ gimel 143211 14.3211% 14.2857%
+daleth 125257 12.5257% 12.5000%
+    he 110849 11.0849% 11.1111%
+   waw  99935  9.9935% 10.0000%
+ zayin  91001  9.1001%  9.0909%
+  heth  63330  6.3330%  6.3456%