Data commit

Task/Parsing-RPN-to-infix-conversion/Go/parsing-rpn-to-infix-conversion.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+    "fmt"
+    "strings"
+)
+
+var tests = []string{
+    "3 4 2 * 1 5 - 2 3 ^ ^ / +",
+    "1 2 + 3 4 + ^ 5 6 + ^",
+}
+
+var opa = map[string]struct {
+    prec   int
+    rAssoc bool
+}{
+    "^": {4, true},
+    "*": {3, false},
+    "/": {3, false},
+    "+": {2, false},
+    "-": {2, false},
+}
+
+const nPrec = 9
+
+func main() {
+    for _, t := range tests {
+        parseRPN(t)
+    }
+}
+
+func parseRPN(e string) {
+    fmt.Println("\npostfix:", e)
+    type sf struct {
+        prec int
+        expr string
+    }
+    var stack []sf
+    for _, tok := range strings.Fields(e) {
+        fmt.Println("token:", tok)
+        if op, isOp := opa[tok]; isOp {
+            rhs := &stack[len(stack)-1]
+            stack = stack[:len(stack)-1]
+            lhs := &stack[len(stack)-1]
+            if lhs.prec < op.prec || (lhs.prec == op.prec && op.rAssoc) {
+                lhs.expr = "(" + lhs.expr + ")"
+            }
+            lhs.expr += " " + tok + " "
+            if rhs.prec < op.prec || (rhs.prec == op.prec && !op.rAssoc) {
+                lhs.expr += "(" + rhs.expr + ")"
+            } else {
+                lhs.expr += rhs.expr
+            }
+            lhs.prec = op.prec
+        } else {
+            stack = append(stack, sf{nPrec, tok})
+        }
+        for _, f := range stack {
+            fmt.Printf("    %d %q\n", f.prec, f.expr)
+        }
+    }
+    fmt.Println("infix:", stack[0].expr)
+}