diff --git a/DataStructures/Stacks/InfixToPostfix.java b/DataStructures/Stacks/InfixToPostfix.java new file mode 100644 index 0000000000000000000000000000000000000000..01fd16210b1809d16e4736aa603e634b060f8d89 --- /dev/null +++ b/DataStructures/Stacks/InfixToPostfix.java @@ -0,0 +1,55 @@ +package DataStructures.Stacks; + +import java.util.Stack; + +public class InfixToPostfix { + public static void main(String[] args) throws Exception { + assert "32+".equals(infix2PostFix("3+2")); + assert "123++".equals(infix2PostFix("1+(2+3)")); + assert "34+5*6-".equals(infix2PostFix("(3+4)*5-6")); + } + + public static String infix2PostFix(String infixExpression) throws Exception { + if (!BalancedBrackets.isBalanced(infixExpression)) { + throw new Exception("invalid expression"); + } + StringBuilder output = new StringBuilder(); + Stack stack = new Stack<>(); + for (char element : infixExpression.toCharArray()) { + if (Character.isLetterOrDigit(element)) { + output.append(element); + } else if (element == '(') { + stack.push(element); + } else if (element == ')') { + while (!stack.isEmpty() && stack.peek() != '(') { + output.append(stack.pop()); + } + stack.pop(); + } else { + while (!stack.isEmpty() && precedence(element) <= precedence(stack.peek())) { + output.append(stack.pop()); + } + stack.push(element); + } + } + while (!stack.isEmpty()) { + output.append(stack.pop()); + } + return output.toString(); + } + + private static int precedence(char operator) { + switch (operator) { + case '+': + case '-': + return 0; + case '*': + case '/': + return 1; + case '^': + return 2; + default: + return -1; + } + } +} \ No newline at end of file