import java.util.*; /** * 2017/09/09 * * Reference: * 1) https://openhome.cc/Gossip/AlgorithmGossip/InFixPostfix.htm#Java * 2) https://github.com/e212156822000/CollegeHomeworkCollection/tree/master/Data-Structure/DSHW1_2A_103403513 * * Description: * If you Submit (2+3)*(5-2) * Output will be * Origin:(2+3)*(5-2) * Postfix:23+52-* * Answer:15 * * Please do not hesitate to leave your suggestions! * */ public class Postfix { static String input; static String postfix; public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.println("Please Enter Formula:"); input = sc.next(); //next() exclude empty character, space and tab while(ParentheseWrong()) { System.out.println("Please Enter Formula Again:"); input = sc.next(); } System.out.println("Origin:"+input); postfix = toPostfix(); System.out.println("Postfix:"+postfix); int answer = evaluate(); System.out.println("Answer:"+answer); } private static boolean ParentheseWrong() { //Stack inputStack = new Stack(); int left = 0, right = 0; for(int i = 0; i < input.length(); i++) { if( input.charAt(i) == '(' ) left++; else if( input.charAt(i) == ')' ) right++; } if (left==right) return false; else return true; } private static String toPostfix() { Stack operatorStack = new Stack(); StringBuilder postfixBuilder = new StringBuilder(); //StringBuilder operandBuilder = new StringBuilder(); for (int i = 0; i < input.length(); i++) { int prior = priority(input.charAt(i)); switch (prior) { case 0: postfixBuilder.append(String.valueOf(input.charAt(i))); break; case 1: //if stack contains top priority of data, pop out all operand first if( (!operatorStack.empty()) ) { int size = operatorStack.size(); for ( int j = 0; j < size; j++ ) { if( operatorStack.peek()=='(' || operatorStack.peek()==')' ) break; postfixBuilder.append(String.valueOf(operatorStack.pop())); } } operatorStack.push(input.charAt(i)); break; case 2: operatorStack.push(input.charAt(i)); break; case 3: if( input.charAt(i) == '(' ) operatorStack.push(input.charAt(i)); else if ( input.charAt(i) == ')' ){ while( operatorStack.peek() != '(' ){ postfixBuilder.append(String.valueOf(operatorStack.pop())); } operatorStack.pop(); //popout '(' } break; } } //pop out remaining data int size = operatorStack.size(); for ( int k = 0; k < size; k++ ) { postfixBuilder.append(String.valueOf(operatorStack.pop())); } //return postfix return postfixBuilder.toString(); } private static int evaluate() { Stack numericStack = new Stack(); for(int i = 0; i < postfix.length(); i++) { int prior = priority(postfix.charAt(i)); if(prior!=0) { int a = Integer.valueOf(numericStack.pop()); int b = Integer.valueOf(numericStack.pop()); int temp = calculate(a, b, Character.toString(postfix.charAt(i))); numericStack.push( String.valueOf(temp) ); //convert integer into String } else { numericStack.push(Character.toString(postfix.charAt(i))); } } return Integer.valueOf(numericStack.pop()); } private static int calculate(int a, int b, String operator) { int temp = 0; switch(operator) { case "+": temp = b+a; break; case "-": temp = b-a; break; case "*": temp = b*a; break; case "/": temp = b/a; break; } return temp; } private static int priority(char value) { return value == '(' || value == ')' ? 3 : value == '*' || value == '/' ? 2 : value == '+' || value == '-' ? 1 : 0 ; } }

Infix To Postfix 2017/09/09