tasks a-s

Task/Parsing-RPN-to-infix-conversion/D/parsing-rpn-to-infix-conversion.d

@@ -0,0 +1,43 @@
+import std.stdio, std.string, std.array;
+
+void parseRPN(in string e) {
+    enum nPrec = 9;
+    static struct Info { int prec; bool rAssoc; }
+    immutable /*static*/ opa = ["^": Info(4, true),
+                                "*": Info(3, false),
+                                "/": Info(3, false),
+                                "+": Info(2, false),
+                                "-": Info(2, false)];
+
+    writeln("\nPostfix input: ", e);
+    static struct Sf { int prec; string expr; }
+    Sf[] stack;
+    foreach (immutable tok; e.split()) {
+        writeln("Token: ", tok);
+        if (tok in opa) {
+            immutable op = opa[tok];
+            immutable rhs = stack.back;
+            stack.popBack();
+            auto lhs = &stack.back;
+            if (lhs.prec < op.prec ||
+                (lhs.prec == op.prec && op.rAssoc))
+                lhs.expr = "(" ~ lhs.expr ~ ")";
+            lhs.expr ~= " " ~ tok ~ " ";
+            lhs.expr ~= (rhs.prec < op.prec ||
+                         (rhs.prec == op.prec && !op.rAssoc)) ?
+                        "(" ~ rhs.expr ~ ")" :
+                        rhs.expr;
+            lhs.prec = op.prec;
+        } else
+            stack ~= Sf(nPrec, tok);
+        foreach (immutable f; stack)
+            writefln(`    %d "%s"`, f.prec, f.expr);
+    }
+    writeln("Infix result: ", stack[0].expr);
+}
+
+void main() {
+    foreach (immutable test; ["3 4 2 * 1 5 - 2 3 ^ ^ / +",
+                              "1 2 + 3 4 + ^ 5 6 + ^"])
+        parseRPN(test);
+}