Design2 complete

Problem1.py

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+"""
+DESIGN QUEUES USING STACKS
+https://leetcode.com/problems/implement-queue-using-stacks/description/
+"""
+
+#Time complexity:
+# push: O(1)
+# pop: O(1)
+# peek: O(1)
+# empty_stack: O(1)
+
+#Space Complexity: O(n)
+class MyQueue(object):
+
+    def __init__(self):
+        # in_stack for enqueue, out_stack for dequeue
+        self.in_stack = []
+        self.out_stack = []
+
+    def push(self, x):
+        """
+        Enqueue element x to the back of queue
+        :type x: int
+        :rtype: None
+        """
+        self.in_stack.append(x)
+
+    def pop(self):
+        """
+        Dequeue element from the front of queue
+        :rtype: int
+        """
+        self._shift_stacks()
+        if not self.out_stack:   # Edge case: queue empty
+            return None
+        return self.out_stack.pop()
+
+    def peek(self):
+        """
+        Get the front element
+        :rtype: int
+        """
+        self._shift_stacks()
+        if not self.out_stack:   # Edge case: queue empty
+            return None
+        return self.out_stack[-1]
+
+    def empty(self):
+        """
+        Returns whether the queue is empty
+        :rtype: bool
+        """
+        return not self.in_stack and not self.out_stack
+
+    def _shift_stacks(self):
+        """
+        Helper function:
+        Move elements from in_stack to out_stack if out_stack is empty
+        Ensures correct FIFO order
+        """
+        if not self.out_stack:  # only shift when out_stack is empty
+            while self.in_stack:
+                self.out_stack.append(self.in_stack.pop())

Problem2.py

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+"""
+DESIGN HASHMAP
+https://leetcode.com/problems/design-hashmap/
+"""
+
+# put(key, value):
+# Traverse linked list in that bucket → O(k), where k = # of nodes in that bucket.
+# Average case (with good hash and large table size): O(1).
+# Worst case (all keys collide into one bucket): O(n).
+
+# get(key):
+# Traverse list in that bucket → O(k).
+# Average: O(1), Worst: O(n)
+
+# remove(key):
+# Traverse list in bucket → O(k).
+# Average: O(1), Worst: O(n).
+
+# Overall average: O(1) (amortized)
+
+class ListNode(object):
+    def __init__(self, key = -1, value = -1, next=None):
+        self.key = key
+        self.value = value
+        self.next = next
+
+class MyHashMap(object):
+
+    def __init__(self):
+        self.size = 10000
+        self.table = [ListNode] * self.size
+
+    def calculate_hash_value(self, key):
+        return key % self.size
+
+    def put(self, key, value):
+        """
+        :type key: int
+        :type value: int
+        :rtype: None
+        """
+        hv = self.calculate_hash_value(key)
+        cur = self.table[hv]
+        while cur.next:
+            if cur.next.key == key:
+                cur.next.value = value
+                return
+            cur = cur.next
+        cur.next = ListNode(key, value)    
+
+    def get(self, key):
+        """
+        :type key: int
+        :rtype: int
+        """
+        hv = self.calculate_hash_value(key)
+        cur = self.table[hv]
+        while cur:
+            if cur.key == key:
+                return cur.value
+            cur = cur.next
+        return -1 
+
+    def remove(self, key):
+        """
+        :type key: int
+        :rtype: None
+        """
+        hv = self.calculate_hash_value(key)
+        cur = self.table[hv]
+        while cur and cur.next:
+            if cur.next.key == key:
+                cur.next = cur.next.next
+                return
+            cur = cur.next
+