A-M baby

Task/24-game-Solve/D/24-game-solve.d

@@ -0,0 +1,47 @@
+import std.stdio, std.algorithm, std.range, std.typecons, std.conv,
+       std.string, permutations2, arithmetic_rational;
+
+string solve(in int target, in int[] problem) {
+  static struct ComputeAllOperations {
+    //static struct T { Rational r; string e; }
+    alias T = Tuple!(Rational,"r", string,"e");
+    Rational[] L;
+
+    int opApply(in int delegate(ref T) dg) {
+      int result;
+
+      if (!L.empty) {
+        auto x = L[0];
+        auto xs = L[1 .. $];
+        if (L.length == 1) {
+          T aux = T(x, text(x));
+          result = dg(aux);
+        } else {
+          OUTER: foreach (o; ComputeAllOperations(xs)) {
+            auto y = o.r;
+            auto sub = [T(x * y, "*"), T(x + y, "+"), T(x - y, "-")];
+            if (y) sub ~= [T(x/y, "/")];
+            foreach (e; sub) {
+              auto aux = T(e.r, format("(%s%s%s)", x, e.e, o.e));
+              result = dg(aux); if (result) break OUTER;
+            }
+          }
+        }
+      }
+
+      return result;
+    }
+  }
+
+
+  foreach (p; problem.map!Rational.array.permutations)
+    foreach (sol; ComputeAllOperations(p))
+      if (sol.r == target)
+        return sol.e;
+  return "No solution";
+}
+
+void main() {
+  foreach (prob; [[6, 7, 9, 5], [3, 3, 8, 8], [1, 1, 1, 1]])
+    writeln(prob, ": ", solve(24, prob));
+}