# Shunting Yard Algorithm in Java

The Shunting Yard algorithm is a commonly used algorithm in computer science for converting infix expressions to postfix or prefix expressions. In postfix notation, also known as Reverse Polish Notation (RPN), the operator is placed after the operands, while in prefix notation, also known as Polish Notation, the operator is placed before the operands. The Shunting Yard algorithm was invented by Edsger Dijkstra in 1961. Here's how the Shunting Yard algorithm works:

• Create two stacks, one for operators and one for output.
• Read each token in the infix expression from left to right.
• If the token is a number, add it to the output stack.
• If the token is an operator, then:
• While there are operators on the operator stack, and the operator on top of the stack has greater or equal precedence than the current operator, pop the operator from the operator stack and add it to the output stack.
• Push the current operator onto the operator stack.
• If the token is a left parenthesis, push it onto the operator stack.
• If the token is a right parenthesis, pop operators from the operator stack and add them to the output stack until a left parenthesis is found. Discard the left parenthesis.
• After all tokens have been read, pop any remaining operators from the operator stack and add them to the output stack.

Let's implement the Shunting Yard algorithm in Java.

ShuntingYard.java

Output:

```Infix expression: 3+4*2/(1-5)^2
Postfix expression: 342*15-2^/+
```

#### Note: In this example, we have implemented the Shunting Yard algorithm to convert the infix expression "3+4*2/(1-5)^2" to postfix notation.

• The algorithm was named "Shunting Yard" because it was originally implemented using a railway shunting yard, which is a system used to sort and reorganize trains in a rail yard.
• The Shunting Yard algorithm is a classic example of a stack-based algorithm, where we use a stack to keep track of operators and operands in the expression.
• The algorithm is efficient, with a time complexity of O(n), where n is the length of the input expression.
• The Shunting Yard algorithm can be used to convert infix expressions to postfix or prefix notation, depending on the order in which operators and operands are arranged.
• The postfix notation is useful for evaluating expressions efficiently, because it eliminates the need for parentheses and operator precedence rules.
• The prefix notation is also useful in some cases, especially in functional programming, where it is used to define expressions as a series of nested function calls.
• The Shunting Yard algorithm can handle multiple operators of the same precedence level, and ensures that they are evaluated in the correct order based on their associativity (left-to-right or right-to-left).
• The algorithm can also handle unary operators, which are operators that act on a single operand, such as the negation (-) operator.
• The Shunting Yard algorithm can be extended to handle more complex expressions, such as those with functions, variables, and arrays.
• One of the key advantages of the Shunting Yard algorithm is that it can handle expressions of arbitrary complexity, including those with nested parentheses and multiple levels of operator precedence.
• Another advantage of the Shunting Yard algorithm is that it can be extended to support new operators and functions with relative ease.
• The Shunting Yard algorithm is based on the idea of converting an infix expression into a postfix or prefix notation, which can then be evaluated using a stack-based approach. This involves scanning the input expression from left to right, and using a stack to keep track of operators and operands as they are encountered.
• One of the key steps in the Shunting Yard algorithm is the process of "shunting" operators onto a stack based on their precedence and associativity. This involves comparing the current operator with the top operator on the stack, and either pushing the current operator onto the stack or popping the top operator off the stack, depending on the relative precedence and associativity of the operators.
• Another important step in the Shunting Yard algorithm is the process of handling parentheses. This involves using a separate stack to keep track of the opening and closing parentheses in the expression, and popping operators off the operator stack until the corresponding opening parentheses is encountered.
• In addition to its use in converting infix expressions to postfix or prefix notation, the Shunting Yard algorithm can also be used for other tasks, such as evaluating arithmetic expressions directly, checking the validity of expressions, and generating code for expression evaluation in programming languages.
• Shunting Yard algorithm is that it provides a way to evaluate arithmetic expressions without requiring nested parentheses or explicit operator precedence rules. This makes it easier to read and understand complex expressions, and can help reduce the likelihood of errors or mistakes.
• The Shunting Yard algorithm is often used in computer programming, particularly in compilers and interpreters for programming languages. By converting expressions to postfix or prefix notation, it can make it easier to generate machine code or interpret code at runtime.
• The Shunting Yard algorithm can also be used in other areas of computer science and engineering, such as robotics, signal processing, and control systems. In these applications, it is often used to evaluate complex mathematical expressions or to generate code for real-time systems.
• One of the limitations of the Shunting Yard algorithm is that it does not handle all types of expressions.
• The Shunting Yard algorithm can also be used to convert postfix expressions back to infix notation. This involves using a stack to keep track of operands and operators as they are encountered, and building the infix expression from the bottom up.
• The Shunting Yard algorithm was first described by Edsger W. Dijkstra in 1961, and has since become a classic example of a stack-based algorithm. It is still widely used today in a variety of applications, and has been extended and modified in many ways to support new types of expressions and problem domains.
• The Shunting Yard algorithm can be modified to handle different types of operators and operands, such as bitwise operators or complex numbers. This involves extending the algorithm to handle additional parsing and evaluation steps, and may require modifying the data structures and algorithms used in the process.
• Another variation of the Shunting Yard algorithm is the Reverse Polish Notation (RPN) algorithm, which is similar to the postfix notation used in the Shunting Yard algorithm but has a slightly different parsing and evaluation process. In RPN, operators are placed after their operands rather than before, and there is no need for parentheses or operator precedence rules.
• The Shunting Yard algorithm can also be used to parse and evaluate boolean expressions, by using logical operators such as AND, OR, and NOT. This involves extending the algorithm to handle boolean operands and operators, and may require additional evaluation rules and data structures.
• In some cases, the Shunting Yard algorithm may be less efficient than other parsing and evaluation methods, such as recursive descent parsing or operator precedence parsing. This is because it requires more stack operations and has a higher overhead for processing parentheses and operator precedence rules.

Overall, the Shunting Yard algorithm is a powerful and flexible tool for working with mathematical expressions, and provides a useful foundation for developing more advanced parsing and evaluation methods. By understanding the principles and techniques behind the Shunting Yard algorithm, developers and engineers can gain insights into the nature of expression parsing and evaluation, and develop more effective and efficient algorithms for a wide range of applications.