chore: Completed precourse-1

Exercise_1.py

@@ -1,24 +1,41 @@
+# Time Complexity : everything is O(1)
+# Space Complexity : O(n)
+# Did this code successfully run on Leetcode : yes
+# Any problem you faced while coding this : no
+
+
+# Your code here along with comments explaining your approach
+
+
 class myStack:
-  #Please read sample.java file before starting.
-  #Kindly include Time and Space complexity at top of each file
-     def __init__(self):
-
-     def isEmpty(self):
-
-     def push(self, item):
-
-     def pop(self):
-
-
-     def peek(self):
-
-     def size(self):
-
-     def show(self):
-
+    # Please read sample.java file before starting.
+    # Kindly include Time and Space complexity at top of each file
+    def __init__(self):
+        self.arr = []
+
+    def isEmpty(self):
+        if len(self.arr) == 0:
+            return True
+        return False
+
+    def push(self, item):
+        self.arr.append(item)
+
+    def pop(self):
+        return self.arr.pop()
+
+    def peek(self):
+        return self.arr[-1]
+
+    def size(self):
+        return len(self.arr)
+
+    def show(self):
+        return self.arr
+
 
 s = myStack()
-s.push('1')
-s.push('2')
+s.push("1")
+s.push("2")
 print(s.pop())
 print(s.show())

Exercise_2.py

@@ -1,32 +1,48 @@
+# Time Complexity : O(1)
+# Space Complexity : O(n)
+# Did this code successfully run on Leetcode : yes
+# Any problem you faced while coding this : no
+
+
+# Your code here along with comments explaining your approach
+
 
 class Node:
     def __init__(self, data):
-       self.data = data
-       self.next = None
-
+        self.data = data
+        self.next = None
+
+
 class Stack:
     def __init__(self):
-
+        self.arr = []
+
     def push(self, data):
-
+        self.arr.append(data)
+
     def pop(self):
-
+        if len(self.arr) == 0:
+            return None
+        return self.arr.pop()
+
+
 a_stack = Stack()
 while True:
-    #Give input as string if getting an EOF error. Give input like "push 10" or "pop"
-    print('push <value>')
-    print('pop')
-    print('quit')
-    do = input('What would you like to do? ').split()
-    #Give input as string if getting an EOF error. Give input like "push 10" or "pop"
+    # Give input as string if getting an EOF error. Give input like "push 10" or "pop"
+    print("push <value>")
+    print("pop")
+    print("quit")
+    do = input("What would you like to do? ").split()
+    # Give input as string if getting an EOF error. Give input like "push 10" or "pop"
+    print(do)
     operation = do[0].strip().lower()
-    if operation == 'push':
+    if operation == "push":
         a_stack.push(int(do[1]))
-    elif operation == 'pop':
+    elif operation == "pop":
         popped = a_stack.pop()
         if popped is None:
-            print('Stack is empty.')
+            print("Stack is empty.")
         else:
-            print('Popped value: ', int(popped))
-    elif operation == 'quit':
+            print("Popped value: ", int(popped))
+    elif operation == "quit":
         break

Exercise_3.py

@@ -1,9 +1,22 @@
+# Time Complexity : O(n)
+# Space Complexity : O(n)
+# Did this code successfully run on Leetcode : yes
+# Any problem you faced while coding this : took me a little bit to warp my head around singly linked list but i think i get it now
+
+
+# Your code here along with comments explaining your approach
+
+
 class ListNode:
     """
     A node in a singly-linked list.
     """
+
     def __init__(self, data=None, next=None):
-
+        self.data = data
+        self.next = next
+
+
 class SinglyLinkedList:
     def __init__(self):
         """
@@ -17,16 +30,67 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
-
+        newNode = ListNode(data)
+        if self.head is None:
+            self.head = newNode
+        else:
+            current = self.head
+            while current.next is not None:
+                current = current.next
+            current.next = newNode
+        return newNode
+
     def find(self, key):
         """
         Search for the first element with `data` matching
         `key`. Return the element or `None` if not found.
         Takes O(n) time.
         """
-
+        current = self.head
+        while current is not None:
+            if current.data == key:
+                return current
+            current = current.next
+        return None
+
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        if self.head.data == key:
+            self.head = self.head.next
+            return
+
+        current = prev = self.head
+        while current is not None:
+            if current.data == key:
+                prev.next = current.next
+                return
+            else:
+                prev = current
+            current = current.next
+
+
+ll = SinglyLinkedList()
+while True:
+    print("append <value>")
+    print("find <value>")
+    print("remove <value>")
+    print("quit")
+    do = input("What would you like to do? ").split()
+    operation = do[0].strip().lower()
+    if operation == "append":
+        ll.append(int(do[1]))
+        print("Appended", do[1])
+    elif operation == "find":
+        result = ll.find(int(do[1]))
+        if result is None:
+            print("Not found.")
+        else:
+            print("Found:", result.data)
+    elif operation == "remove":
+        ll.remove(int(do[1]))
+        print("Removed", do[1])
+    elif operation == "quit":
+        break