Create EvalutatePostFix.java

A Program To Evaluate The PostFix Expression Using Stack Data Structure Using Java

Author: akashSky369

EvalutatePostFix.java

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+ //Input: tokens = ["2","1","+","3","*"]
+//Output: 9
+//Explanation: ((2 + 1) * 3) = 9
+
+public int evalRPN(String[] tokens) {
+        Stack<String> stack = new Stack<>();
+        for(String s : tokens){
+            if(Objects.equals(s, "+") || Objects.equals(s, "-") || Objects.equals(s, "/") || Objects.equals(s, "*")){
+
+                if(s.equals("+")){
+                    int first = Integer.parseInt(stack.pop());
+                    int second = Integer.parseInt(stack.pop());
+                    int n = second+first;
+                    stack.push(Integer.toString(n));
+                }
+
+                else if(s.equals("-")){
+                    int first = Integer.parseInt(stack.pop());
+                    int second = Integer.parseInt(stack.pop());
+                    int n = second-first;
+
+                    stack.push(Integer.toString(n));
+                }
+
+                else if(s.equals("*")){
+                    int first = Integer.parseInt(stack.pop());
+                    int second = Integer.parseInt(stack.pop());
+                    int n = second*first;
+
+                    stack.push(Integer.toString(n));
+                }
+                else if(s.equals("/")){
+                    int first = Integer.parseInt(stack.pop());
+                    int second = Integer.parseInt(stack.pop());
+                    int n = second/first;
+
+                    stack.push(Integer.toString(n));
+                }
+            }
+            else{
+                stack.push(s);
+            }
+        }
+        return Integer.parseInt(stack.pop());
+    }