Merge pull request #2395 from Xceptions/browserhistory

Browser History Operations

Author: geekcomputers

BrowserHistory/backend.py

@@ -0,0 +1,81 @@
+class DLL:
+    """
+        a doubly linked list that holds the current page,
+        next page, and previous page.
+        Used to enforce order in operations
+    """
+    def __init__(self, val: str =None):
+        self.val = val
+        self.nxt = None
+        self.prev = None
+
+
+class BrowserHistory:
+    """
+    This class designs the operations of a browser history
+
+    It works by using a doubly linked list to hold the urls
+    """
+
+    def __init__(self, homepage: str):
+        """
+        Returns - None
+        Input - None
+        ----------
+        - Initialize doubly linked list which will serve as the
+            browser history and sets the current page
+        """
+        self.head = DLL(homepage)
+        self.curr = self.head
+        
+    def visit(self, url: str) -> None:
+        """
+        Returns - None
+        Input - str
+        ----------
+        - Adds the current url to the DLL
+        - sets both the next and previous values
+        """
+        url_node = DLL(url)
+        self.curr.nxt = url_node
+        url_node.prev = self.curr
+        
+        self.curr = url_node
+        
+
+    def back(self, steps: int) -> str:
+        """
+        Returns - str
+        Input - int
+        ----------
+        - Iterates through the DLL backwards `step` number of times
+        - returns the appropriate value
+        """
+        while steps > 0 and self.curr.prev:
+            self.curr = self.curr.prev
+            steps -= 1
+        return self.curr.val
+        
+
+    def forward(self, steps: int) -> str:
+        """
+        Returns - str
+        Input - int
+        ----------
+        - Iterates through the DLL forewards `step` number of times
+        - returns the appropriate value
+        """
+        while steps > 0 and self.curr.nxt:
+            self.curr = self.curr.nxt
+            steps -= 1
+        return self.curr.val
+        
+
+if __name__ == "__main__":
+    obj = BrowserHistory("google.com")
+    obj.visit("twitter.com")
+    param_2 = obj.back(1)
+    param_3 = obj.forward(1)
+
+    print(param_2)
+    print(param_3)