DSA using JavaScript

Input: &quot;A+B*C&quot; Output : &quot;ABC*+&quot;
Input: &quot;A*B+C&quot; Output : &quot;AB*C+&quot;
Input: &quot;A*(B+C)&quot; Output : &quot;ABC+*&quot;

Stack

class Stack {
    constructor() {
        this.items = [];
    }

    push(element) {
        this.items.push(element);
    }

    pop() {
        if (this.isEmpty()) return null;
        return this.items.pop();
    }

    peek() {
        if (this.isEmpty()) return null;
        return this.items[this.items.length - 1];
    }

    isEmpty() {
        return this.items.length === 0;
    }

    size() {
        return this.items.length;
    }

    clear() {
        this.items = [];
    }
}

function infixToPostfix(expression) {
    const stack = new Stack();
    let postfix = '';
    const precedence = {
        '+': 1,
        '-': 1,
        '*': 2,
        '/': 2
    };

    for (let char of expression) {
        if (/[A-Za-z0-9]/.test(char)) {  // If operand, add directly to postfix
            postfix += char;
        } else if (char === '(') {       // Push '(' to stack
            stack.push(char);
        } else if (char === ')') {       // Pop until '('
            while (!stack.isEmpty() && stack.peek() !== '(') {
                postfix += stack.pop();
            }
            stack.pop(); // Remove '('
        } else {  // Operator
            while (!stack.isEmpty() && precedence[char] <= precedence[stack.peek()]) {
                postfix += stack.pop();
            }
            stack.push(char);
        }
    }

    // Pop remaining operators
    while (!stack.isEmpty()) {
        postfix += stack.pop();
    }

    return postfix;
}

// Sample Usage
console.log(infixToPostfix("A+B"));        // Output: "AB+"
console.log(infixToPostfix("A+B*C"));      // Output: "ABC*+"
console.log(infixToPostfix("A*B+C"));      // Output: "AB*C+"
console.log(infixToPostfix("A*(B+C)"));    // Output: "ABC+*"