CDE

Task/Evolutionary-algorithm/D/evolutionary-algorithm-2.d

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+import std.stdio, std.random, std.algorithm, std.range;
+
+enum target = "METHINKS IT IS LIKE A WEASEL"d;
+enum C = 100;  // Number of children in each generation.
+enum P = 0.05; // Mutation probability.
+auto alphabet = " ABCDEFGHIJLKLMNOPQRSTUVWXYZ"d.dup;
+const fitness = (dchar[] s) => count!"a[0] != a[1]"(zip(s, target));
+const rndc = () => alphabet[uniform(0, $)];
+const mutate = (dchar[] s) =>
+               s.map!(a => uniform(0., 1.) < P ? rndc() : a)().array();
+
+void main() {
+  auto parent = target.length.iota().map!(_ => rndc())().array();
+  for (int gen = 1; parent != target; gen++) {
+    auto offs = parent.repeat(C).map!mutate().array();
+    parent = offs.minPos!((a, b) => fitness(a) < fitness(b))()[0];
+    writefln("Gen %2d, dist=%2d: %s", gen, fitness(parent), parent);
+  }
+}