From 31243c405d960775a5d9c0162db38aec25278e69 Mon Sep 17 00:00:00 2001
From: satvik <svsgoyal@gmail.com>
Date: Thu, 8 Oct 2020 21:36:25 +0530
Subject: [PATCH 1/2] Create PostFixEval.java

---
 Coding/Java/PostFixEval.java | 94 ++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 Coding/Java/PostFixEval.java

diff --git a/Coding/Java/PostFixEval.java b/Coding/Java/PostFixEval.java
new file mode 100644
index 0000000..e64306a
--- /dev/null
+++ b/Coding/Java/PostFixEval.java
@@ -0,0 +1,94 @@
+import java.util.*;
+
+class CQStack
+{
+  public int maxSize; // size of stack array
+  public int[] stackArray;
+  public int top; // top of stack
+
+  public CQStack(int s) // constructor
+  {
+    maxSize = s; // set array size
+    stackArray = new int[maxSize]; // create array
+    top = -1; // no items yet
+  }
+  public boolean isEmpty() // true if stack is empty
+  {
+    return (top == -1);
+  }
+  public boolean isFull() // true if stack is full
+  {
+    return (top == maxSize-1);
+  }
+
+  public void push(int j) // put item on top of stack
+  {
+    if(isFull())
+    {
+    }
+    else
+    {
+      stackArray[++top] = j; // increment top, insert item
+    }
+  }
+  public int pop() // take item from top of stack
+  {
+    if (isEmpty())
+    {
+      return -1;
+    }
+    else
+    {
+      int temp=stackArray[top--];
+      return temp; // access item, decrement top
+    }
+  }
+}
+
+public class PostFixEval
+{
+    
+    static int evalPostfix(CQStack s, String exp)
+{
+    int i, op1, op2, answer;
+    for (i = 0; i < exp.length(); ++i)
+    {
+    
+      char c = exp.charAt(i);
+      if (Character.isDigit(c))
+        s.push(c - '0');
+
+      else
+      {
+        op2 = s.pop();
+        op1 = s.pop();
+        switch(c)
+        {
+          case '+': s.push(op1 + op2); break;
+          case '-': s.push(op1 - op2); break;
+          case '*': s.push(op1 * op2); break;
+          case '/': s.push(op1 / op2); break;
+          case '^': s.push((int)Math.pow(op1,op2)); break;
+        }
+      }
+    }
+    answer = s.pop();
+    return answer;
+}
+
+
+public static void main(String[] args)
+  {
+    CQStack theStack = new CQStack(100); // make new stack
+    Scanner s=new Scanner(System.in);
+    int t, n, q1, q2;
+    String st;
+    t = Integer.parseInt(s.nextLine());
+    while(t>0)
+    {
+      st = s.nextLine();
+      System.out.println(evalPostfix(theStack, st));
+      t--;
+    }
+  }
+}
\ No newline at end of file

From e0511ba0e7eb8f7a85a941282c6abb461d7b2419 Mon Sep 17 00:00:00 2001
From: satvik <svsgoyal@gmail.com>
Date: Thu, 8 Oct 2020 21:36:36 +0530
Subject: [PATCH 2/2] Create PreFixEval.java

---
 Coding/Java/PreFixEval.java | 94 +++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 Coding/Java/PreFixEval.java

diff --git a/Coding/Java/PreFixEval.java b/Coding/Java/PreFixEval.java
new file mode 100644
index 0000000..1609749
--- /dev/null
+++ b/Coding/Java/PreFixEval.java
@@ -0,0 +1,94 @@
+import java.util.*;
+
+class CQStack
+{
+  public int maxSize; // size of stack array
+  public int[] stackArray;
+  public int top; // top of stack
+
+  public CQStack(int s) // constructor
+  {
+    maxSize = s; // set array size
+    stackArray = new int[maxSize]; // create array
+    top = -1; // no items yet
+  }
+  public boolean isEmpty() // true if stack is empty
+  {
+    return (top == -1);
+  }
+  public boolean isFull() // true if stack is full
+  {
+    return (top == maxSize-1);
+  }
+
+  public void push(int j) // put item on top of stack
+  {
+    if(isFull())
+    {
+    }
+    else
+    {
+      stackArray[++top] = j; // increment top, insert item
+    }
+  }
+  public int pop() // take item from top of stack
+  {
+    if (isEmpty())
+    {
+      return -1;
+    }
+    else
+    {
+      int temp=stackArray[top--];
+      return temp; // access item, decrement top
+    }
+  }
+}
+
+class Result {
+  static int evalPrefix(CQStack s, String exp) {
+        int i, op1, op2, answer;
+    for (i = exp.length()-1; i >= 0 ; i--)
+    {
+      // If the scanned character is an operand (number here), push it to the stack.
+      char c = exp.charAt(i);
+      if (Character.isDigit(c))
+        s.push(c - '0');
+
+      // If the scanned character is an operator, pop two elements from stack apply the operator
+      else
+      {
+        op1 = s.pop();
+        op2 = s.pop();
+        switch(c)
+        {
+          case '+': s.push(op1 + op2); break;
+          case '-': s.push(op1 - op2); break;
+          case '*': s.push(op1 * op2); break;
+          case '/': s.push(op1 / op2); break;
+          case '^': s.push((int)Math.pow(op1,op2)); break;
+        }
+      }
+    }
+    answer = s.pop();
+    return answer;
+  }
+}
+
+class PreFixEval
+{
+  public static void main(String[] args)
+  {
+    CQStack theStack = new CQStack(100); // make new stack
+    Scanner s=new Scanner(System.in);
+    int t, n, q1, q2;
+    String st;
+    t = Integer.parseInt(s.nextLine());
+    while(t>0)
+    {
+      st = s.nextLine();
+      System.out.println(Result.evalPrefix(theStack, st));
+      t--;
+    }
+  }
+}
\ No newline at end of file