update

Author: Blooverh

DataAndAlgoL/Chp3LinkedLists/Problem44.java

@@ -12,30 +12,30 @@ public static void main(String[] args) {
 
     }
 
-    public ListNode getJosephusPosition(int N, int M){
-        ListNode p;
-        ListNode q;
-        //create circular linked list containing all the players
-        p.setData(1);
+//     public ListNode getJosephusPosition(int N, int M){
+//         ListNode p;
+//         ListNode q;
+//         //create circular linked list containing all the players
+//         p.setData(1);
 
-        q=p;
+//         q=p;
 
-        for(int i=2; i<= N; i++){
-            p=p.getNext();
-            p.setData(i);
-        }
+//         for(int i=2; i<= N; i++){
+//             p=p.getNext();
+//             p.setData(i);
+//         }
 
-        p.setNext(q); // Close the circular linked list by having the last node point to the first
+//         p.setNext(q); // Close the circular linked list by having the last node point to the first
 
-        for(int count=N; count >1; count--){
-            for(int i=0; i<M-1; i++){
-                p=p.getNext();
-                p.setNext(p.getNext().getNext());// remove the eliminated player from the list 
-            }
-        }
+//         for(int count=N; count >1; count--){
+//             for(int i=0; i<M-1; i++){
+//                 p=p.getNext();
+//                 p.setNext(p.getNext().getNext());// remove the eliminated player from the list 
+//             }
+//         }
 
-        return p;
+//         return p;
 
 
-    }
+//     }
 }

DataAndAlgoL/Chpt4Stacks/postFixEval.java

@@ -0,0 +1,33 @@
+package DataAndAlgoL.Chpt4Stacks;
+
+import java.util.Stack;
+
+public class postFixEval {
+    public static void main(String[] args) {
+        
+    }
+
+    public static int postFix(String[] tokens){
+        Stack<Integer> stack= new Stack<>();
+
+        for(String token: tokens){
+            if(token.equals("*")){
+                int res= stack.pop() * stack.pop();
+                stack.push(res);
+            }else if(token.equals("/")){
+                int res=stack.pop() / stack.pop();
+                stack.push(res);
+            }else if(token.equals("+")){
+                int res= stack.pop() + stack.pop();
+                stack.push(res);
+            }else if(token.equals("-")){
+                int res= stack.pop() - stack.pop();
+                stack.push(res);
+            }else{
+                stack.push(Integer.parseInt(token));
+            }
+        }
+
+        return stack.pop();
+    }
+}

LeetCode/Grind169/Stacks/BackSpaceStringCompare_844.java

@@ -5,17 +5,45 @@
 
 public class BackSpaceStringCompare_844 {
     public static void main(String[] args) {
-        Scanner kbr= new Scanner(System.in);
-        System.out.println("Type 1st string: ");
-        String s = kbr.nextLine();
-        System.out.println("Enter 2nd String: ");
-        String t= kbr.nextLine();
+        try (Scanner kbr = new Scanner(System.in)) {
+            System.out.println("Type 1st string: ");
+            String s = kbr.nextLine();
+            System.out.println("Enter 2nd String: ");
+            String t= kbr.nextLine();
 
-        boolean check= backspaceCompare(s, t);
-        System.out.println(check);
+            boolean check= backspaceCompare(s, t);
+            System.out.println(check);
+        }
     }
 
     public static boolean backspaceCompare(String s, String t) {
-        
+         //Maintain 2 stacks for each string which contain the final resultant string  
+         Stack<Character> stack1= new Stack<>();
+         Stack<Character> stack2= new Stack<>();
+ 
+         //iterate character by character and put them in stacks 
+         for(char ch: s.toCharArray()){
+             if(ch == '#'){
+                 if(!stack1.isEmpty()){
+                     stack1.pop();
+                 }
+                 continue;
+             }
+             stack1.push(ch);
+         }
+ 
+         for(char cl: t.toCharArray()){
+             if(cl == '#'){
+                 if(!stack2.isEmpty()){
+                     stack2.pop();
+                 }
+                 continue;
+             }
+             stack2.push(cl);
+         }
+
+         //use stack JAVA ADT comparison method to compare both stacks and return boolean
+         return stack1.equals(stack2);
+ 
     }
 }

LeetCode/Grind169/Stacks/ReversePolishNotation_150.java

@@ -0,0 +1,37 @@
+package Grind169.Stacks;
+
+import java.util.Stack;
+
+public class ReversePolishNotation_150 {
+    public static void main(String[] args) {
+        
+    }
+
+    public static int evalRPN(String[] tokens) {
+        //When we have an operator we pop the last 2 numbers and add them to the stack again.
+        int a,b;
+		Stack<Integer> S = new Stack<Integer>();
+		for (String s : tokens) {
+			if(s.equals("+")) {
+				S.add(S.pop()+S.pop());
+			}
+			else if(s.equals("/")) {
+				b = S.pop();
+				a = S.pop();
+				S.add(a / b);
+			}
+			else if(s.equals("*")) {
+				S.add(S.pop() * S.pop());
+			}
+			else if(s.equals("-")) {
+				b = S.pop();
+				a = S.pop();
+				S.add(a - b);
+			}
+			else {
+				S.add(Integer.parseInt(s));
+			}
+		}	
+		return S.pop();
+	}
+}