From b75156a4d44198eab8d87ad3f87aaedf0180d4f6 Mon Sep 17 00:00:00 2001
From: Xawirses <xawirses@gmail.com>
Date: Tue, 7 Mar 2017 12:57:49 +0100
Subject: [PATCH] Add Read & infix to prefix algo

---
 src/Expression.java | 109 ++++++++++++++++++++++++++++++++++++++++++++
 src/Operator.java   |   9 ++++
 2 files changed, 118 insertions(+)
 create mode 100644 src/Expression.java
 create mode 100644 src/Operator.java

diff --git a/src/Expression.java b/src/Expression.java
new file mode 100644
index 0000000..f027596
--- /dev/null
+++ b/src/Expression.java
@@ -0,0 +1,109 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Stack;
+
+/**
+* Created by xawirses on 28/02/17.
+ */
+public class Expression {
+    private String expression;
+
+    public Expression(){
+        readExpression();
+        parse();
+    }
+
+    public void readExpression(){
+        try {
+            BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));
+            expression = buff.readLine();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private String reverseExpression(String exp) {
+        String reverse = "";
+        for (int i = exp.length()-1; i >= 0; i--) {
+            char c = exp.charAt(i);
+            switch (c) {
+                case '(':
+                    reverse += ")";
+                break;
+
+                case ')':
+                    reverse += "(";
+                break;
+
+                default:
+                    reverse += c;
+            }
+
+        }
+        return reverse;
+    }
+
+    private boolean isParenthesis(char c) {
+        return c == '(' || c == ')';
+    }
+
+    private boolean isOperator(char c) {
+        for (int i = 0; i < Operator.nbOperators; i++) {
+            if(Operator.operators[i] == c)
+                return true;
+        }
+        return false;
+    }
+
+    private boolean isHighterOperator(char current, char stack) {
+        int pCurrent = 0;
+        int pStack = 0;
+
+        for (int i = 0; i < Operator.nbOperators; i++) {
+            if(Operator.operators[i] == current)
+                pCurrent = i;
+            if(Operator.operators[i] == stack)
+                pStack = i;
+        }
+        return (pCurrent >= pStack);
+    }
+
+    private void parse() {
+        String reverse = reverseExpression(expression);
+        String reversePrefix = "";
+
+        LinkedList<String> stack = new LinkedList<String>();
+        for (int i = 0; i < reverse.length(); i++) {
+            char c = reverse.charAt(i);
+            if (!isOperator(c)) {
+                reversePrefix += c;
+            } else if(c == '(') {
+                stack.addLast(String.valueOf(c));
+            } else if(isOperator(c) && !isParenthesis(c)) {
+                while (!stack.isEmpty() && !isParenthesis(stack.peekLast().charAt(0)) && isHighterOperator(c, stack.peekLast().charAt(0))) {
+                    reversePrefix += stack.pollLast();
+                }
+                stack.addLast(String.valueOf(c));
+            } else if(c == ')') {
+                while (!stack.peekLast().equals("(")) {
+                    System.out.println(reversePrefix);
+                    System.out.println(stack.peekLast());
+                    reversePrefix += stack.pollLast();
+                }
+                stack.pollLast();
+            } else {
+                System.err.println("WTF !!");
+            }
+        }
+        while (!stack.isEmpty())
+            reversePrefix += stack.pollLast();
+        System.out.println(reverseExpression(reversePrefix));
+    }
+
+    public static void main(String[] args) {
+        Expression e = new Expression();
+    }
+}
diff --git a/src/Operator.java b/src/Operator.java
new file mode 100644
index 0000000..a67a124
--- /dev/null
+++ b/src/Operator.java
@@ -0,0 +1,9 @@
+/**
+ * Created by xawirses on 28/02/17.
+ */
+
+public class Operator {
+
+    public static final int nbOperators = 9;
+    public static final char operators[] = {'!', 'L', 'M', '(', ')', '&', '|', '>', '='};
+}
\ No newline at end of file