Added solution for Google-SimpleCalculator

README.md

@@ -20,7 +20,7 @@ Maximum In A Stack | Twitter | [MaximumInAStack.java](https://github.com/emafazi
 Number of Ways to Climb Stairs | LinkedIn | [ClimbingStairs.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/linkedin/ClimbingStairs.java) | Done |
 Find Pythagorean Triplets | Uber | [FindPythagoreanTriplets.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/uber/FindPythagoreanTriplets.java) | Done |
 Edit Distance | Airbnb | [EditDistance.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/airbnb/EditDistance.java) | To Do |
-Create a Simple Calculator | Google | [CreateASimpleCalculator.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/google/CreateASimpleCalculator.java) | To Do |
+Create a Simple Calculator | Google | [CreateASimpleCalculator.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/google/CreateASimpleCalculator.java) | Done |
 Longest Sequence with Two Unique Numbers | Facebook | [LongestSequenceWithTwoUniqueNumbers.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/facebook/LongestSequenceWithTwoUniqueNumbers.java) | To Do |
 Find Cycles in a Graph | Facebook | [FindCyclesInAGraph.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/facebook/FindCyclesInAGraph.java) | To Do |
 Word Search | Amazon | [WordSearch.java](https://github.com/emafazillah/DailyInterviewProJava/blob/master/src/main/java/com/dailyinterviewprojava/amazon/WordSearch.java) | Done |

src/main/java/com/dailyinterviewprojava/google/CreateASimpleCalculator.java

@@ -1,4 +1,6 @@
 package com.dailyinterviewprojava.google;
+import java.util.Stack;
+import java.util.Scanner; 
 
 /**
  * 
@@ -11,6 +13,116 @@
  * Output: -4
  *
  */
+
 public class CreateASimpleCalculator {
 
+    static Stack<Integer> numbersStack = new Stack<>();
+    static Stack<String> operationStack = new Stack<>();
+
+    public static void main(String[] args) {
+        Scanner myObj = new Scanner(System.in);  // Create a Scanner object
+        System.out.println("Enter expression");
+        String userExpression = myObj.nextLine();  // Read user input
+        System.out.println("Expression is: " + userExpression); 
+        System.out.println(eval(userExpression));
+    }
+
+    private static int eval(String expression) {
+        String[] splittedArr = expression.split(" ");
+        for (int i = 0; i < splittedArr.length; i++) {
+            String val = splittedArr[i];
+            if (isNum(val)) {
+                numbersStack.push(Integer.valueOf(val));
+            } else if (val.equals("(")) {
+                operationStack.push(val);
+            } else if (val.equals(")")) {
+                while (operationStack.size() > 0 && !operationStack.get(operationStack.size() - 1).equals("(")) {
+                    doOperation();
+                }
+                operationStack.pop();
+            } else if (isOperator(val)) {
+                if (operationStack.size() > 0 && priority(operationStack.get(operationStack.size() - 1)) > priority(val)) {
+                    doOperation();
+                }
+                operationStack.push(val);
+            }
+
+        }
+
+        // here we done with operations between ( )
+        if (numbersStack.size() > 1) {
+            while (operationStack.size() > 0) {
+                doOperation();
+            }
+        } else if (numbersStack.size() == 1) {
+            doOperationSingleNum();
+
+        }
+        return numbersStack.pop();
+    }
+
+    private static void doOperationSingleNum() {
+        String operator = operationStack.pop();
+        Integer num = numbersStack.pop();
+
+        if (operator.equals("-")) {
+            num = -num;
+        }
+        numbersStack.push(num);
+    }
+
+    private static int priority(String val) {
+        int priority;
+        switch (val) {
+            case "+":
+            case "-":
+                priority = 1;
+                break;
+            case "*":
+            case "/":
+                priority = 2;
+                break;
+            default:
+                priority = 0;
+                break;
+        }
+        return priority;
+    }
+
+    private static boolean isOperator(String val) {
+        return val.equals("+") || val.equals("-") || val.equals("*") || val.equals("/");
+    }
+
+    private static void doOperation() {
+        if (numbersStack.size() == 1) {
+            doOperationSingleNum();
+        } else {
+            Integer firstNum = numbersStack.pop();
+            Integer lastNum = numbersStack.pop();
+            String operator = operationStack.pop();
+
+            int result = 0;
+            switch (operator) {
+                case "+":
+                    result = lastNum + firstNum;
+                    break;
+                case "-":
+                    result = lastNum - firstNum;
+                    break;
+                case "*":
+                    result = lastNum * firstNum;
+                    break;
+                case "/":
+                    result = lastNum / firstNum;
+                    break;
+            }
+            numbersStack.push(result);
+        }
+
+    }
+
+    private static boolean isNum(String val) {
+        return "0123456789".contains(val);
+    }
 }
+