Task: Parsing_Shunting-yard algorithm



C#: using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main() {
        string infix = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3";
        Console.WriteLine(infix.ToPostfix());
    }
}

public static class ShuntingYard
{
    private static readonly Dictionary<string, (string symbol, int precedence, bool rightAssociative)> operators
        = new (string symbol, int precedence, bool rightAssociative) [] {
            ("^", 4, true),
            ("*", 3, false),
            ("/", 3, false),
            ("+", 2, false),
            ("-", 2, false)
    }.ToDictionary(op => op.symbol);

    public static string ToPostfix(this string infix) {
        string[] tokens = infix.Split(' ');
        var stack = new Stack<string>();
        var output = new List<string>();
        foreach (string token in tokens) {
            if (int.TryParse(token, out _)) {
                output.Add(token);
                Print(token);
            } else if (operators.TryGetValue(token, out var op1)) {
                while (stack.Count > 0 && operators.TryGetValue(stack.Peek(), out var op2)) {
                    int c = op1.precedence.CompareTo(op2.precedence);
                    if (c < 0 || !op1.rightAssociative && c <= 0) {
                        output.Add(stack.Pop());
                    } else {
                        break;
                    }
                }
                stack.Push(token);
                Print(token);
            } else if (token == "(") {
                stack.Push(token);
                Print(token);
            } else if (token == ")") {
                string top = "";
                while (stack.Count > 0 && (top = stack.Pop()) != "(") {
                    output.Add(top);
                }
                if (top != "(") throw new ArgumentException("No matching left parenthesis.");
                Print(token);
            }
        }
        while (stack.Count > 0) {
            var top = stack.Pop();
            if (!operators.ContainsKey(top)) throw new ArgumentException("No matching right parenthesis.");
            output.Add(top);
        }
        Print("pop");
        return string.Join(" ", output);
        
        
        void Print(string action) => Console.WriteLine($"{action + ":",-4} {$"stack[ {string.Join(" ", stack.Reverse())} ]",-18} {$"out[ {string.Join(" ", output)} ]"}");
        
        void Print(string action) => Console.WriteLine("{0,-4} {1,-18} {2}", action + ":", $"stack[ {string.Join(" ", stack.Reverse())} ]", $"out[ {string.Join(" ", output)} ]");
    }
}



Java: import java.util.Stack;

public class ShuntingYard {

    public static void main(String[] args) {
        String infix = "3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3";
        System.out.printf("infix:   %s%n", infix);
        System.out.printf("postfix: %s%n", infixToPostfix(infix));
    }

    static String infixToPostfix(String infix) {
        
        final String ops = "-+/*^";

        StringBuilder sb = new StringBuilder();
        Stack<Integer> s = new Stack<>();

        for (String token : infix.split("\\s")) {
            if (token.isEmpty())
                continue;
            char c = token.charAt(0);
            int idx = ops.indexOf(c);

            
            if (idx != -1) {
                if (s.isEmpty())
                    s.push(idx);
          
                else {
                    while (!s.isEmpty()) {
                        int prec2 = s.peek() / 2;
                        int prec1 = idx / 2;
                        if (prec2 > prec1 || (prec2 == prec1 && c != '^'))
                            sb.append(ops.charAt(s.pop())).append(' ');
                        else break;
                    }
                    s.push(idx);
                }
            } 
            else if (c == '(') {
                s.push(-2); 
            } 
            else if (c == ')') {
                
                while (s.peek() != -2)
                    sb.append(ops.charAt(s.pop())).append(' ');
                s.pop();
            }
            else {
                sb.append(token).append(' ');
            }
        }
        while (!s.isEmpty())
            sb.append(ops.charAt(s.pop())).append(' ');
        return sb.toString();
    }
}