Data commit

Task/Parsing-RPN-to-infix-conversion/Java/parsing-rpn-to-infix-conversion.java

@@ -0,0 +1,64 @@
+import java.util.Stack;
+
+public class PostfixToInfix {
+
+    public static void main(String[] args) {
+        for (String e : new String[]{"3 4 2 * 1 5 - 2 3 ^ ^ / +",
+            "1 2 + 3 4 + ^ 5 6 + ^"}) {
+            System.out.printf("Postfix : %s%n", e);
+            System.out.printf("Infix : %s%n", postfixToInfix(e));
+            System.out.println();
+        }
+    }
+
+    static String postfixToInfix(final String postfix) {
+
+        class Expression {
+            final static String ops = "-+/*^";
+
+            String op, ex;
+            int prec = 3;
+
+            Expression(String e) {
+                ex = e;
+            }
+
+            Expression(String e1, String e2, String o) {
+                ex = String.format("%s %s %s", e1, o, e2);
+                op = o;
+                prec = ops.indexOf(o) / 2;
+            }
+
+            @Override
+            public String toString() {
+                return ex;
+            }
+        }
+
+        Stack<Expression> expr = new Stack<>();
+
+        for (String token : postfix.split("\\s+")) {
+            char c = token.charAt(0);
+            int idx = Expression.ops.indexOf(c);
+            if (idx != -1 && token.length() == 1) {
+
+                Expression r = expr.pop();
+                Expression l = expr.pop();
+
+                int opPrec = idx / 2;
+
+                if (l.prec < opPrec || (l.prec == opPrec && c == '^'))
+                    l.ex = '(' + l.ex + ')';
+
+                if (r.prec < opPrec || (r.prec == opPrec && c != '^'))
+                    r.ex = '(' + r.ex + ')';
+
+                expr.push(new Expression(l.ex, r.ex, token));
+            } else {
+                expr.push(new Expression(token));
+            }
+            System.out.printf("%s -> %s%n", token, expr);
+        }
+        return expr.peek().ex;
+    }
+}