Prefix

Author: RezaGooner

Prefix/Prefix.cpp

@@ -0,0 +1,136 @@
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+const int MAX_SIZE = 100;
+
+struct Stack {
+    int top; // index of top of stack
+    string elements[MAX_SIZE];
+};
+
+bool isEmpty(Stack& stack) {
+    if (stack.top == -1) {
+        return true;
+    }
+    return false;
+}
+
+bool isFull(Stack& stack) {
+    if (stack.top == MAX_SIZE - 1) {
+        return true;
+    }
+    return false;
+}
+
+void push(Stack& stack, string value) {
+    if (isFull(stack)) {
+        cout << "Stack overflow!" << endl;
+        return;
+    }
+    stack.elements[++stack.top] = value;
+}
+
+void pop(Stack& stack) {
+    if (isEmpty(stack)) {
+        cout << "Stack underflow!" << endl;
+        return;
+    }
+    stack.elements[stack.top--] = "";
+}
+
+string top(Stack& stack) {
+    if (isEmpty(stack)) {
+        // cout << "Stack is empty!" << endl;
+        return "";
+    }
+    return stack.elements[stack.top];
+}
+
+bool isOperator(char c) {
+    return (c == '+' || c == '-' || c == '*' || c == '/');
+}
+
+int getPrecedence(char op) {
+    if (op == '+' || op == '-')
+        return 1;
+    else if (op == '*' || op == '/')
+        return 2;
+    return 0;
+}
+
+string removeSpaces(string str) {
+    string result;
+    for (int i = 0 ; i < str.size() ; i++) {
+        if (str[i] != ' ') {
+            result += str[i];
+        }
+    }
+    return result;
+}
+
+string prefix(Stack& stack ,string infixExpression) {
+    string prefixExpression;
+    for (int i = infixExpression.size() - 1; i >= 0; i--) {
+        char currentChar = infixExpression[i];
+        if (currentChar == ')' || currentChar == '}' || currentChar == ']') {
+            string str(1, currentChar);
+            push(stack, str);
+        } else if (isOperator(currentChar)) {
+            while (!isEmpty(stack) && isOperator(top(stack)[0]) && getPrecedence(currentChar) <= getPrecedence(top(stack)[0])) {
+                prefixExpression += top(stack) + " ";
+                pop(stack);
+            }
+            string str(1, currentChar);
+            push(stack, str);
+        } else if (currentChar == '(' || currentChar == '{' || currentChar == '[') {
+            while (!isEmpty(stack) && isOperator(top(stack)[0])) {
+                prefixExpression += top(stack) + " ";
+                pop(stack);
+            }
+            pop(stack); // remove corresponding closing parenthesis
+        } else {
+            string operand;
+            while ( (i >= 0 && isdigit(infixExpression[i])) || (i >= 0 && isalpha(infixExpression[i]) ))  {
+                operand = infixExpression[i] + operand;
+                i--;
+            } 
+            // reverse
+			string tempOp ; 
+            for (int i = operand.size() -1 ; i >= 0 ; i--){
+            	tempOp += operand[i] ;
+			}
+			
+            i++; // adjust the index after the loop
+            prefixExpression += tempOp + " ";
+        }
+    }
+    while (!isEmpty(stack)) {
+        prefixExpression += top(stack) + " ";
+        pop(stack);
+    }
+    // Reverse the prefix expression
+    string reversedPrefixExpression;
+    for (int i = prefixExpression.size() - 1; i >= 0; i--) {
+        reversedPrefixExpression += prefixExpression[i];
+    }
+    return reversedPrefixExpression;
+}
+
+int main() {
+	Stack stack;
+    stack.top = -1;
+    string infixExpression;
+    cout << "Enter the infix phrase: ";
+    getline(cin, infixExpression);
+
+    cout << prefix(stack , removeSpaces(infixExpression)) ;
+
+    return 0;
+}
+
+/*
+    Reza Asadi (Github : RezaGooner)
+	1402/08/24 ~ 2023/11/15
+*/