A stack implementation that tracks min/max element in constant time

data_structures/stacks/stack_tracking_min_max.py

@@ -0,0 +1,145 @@
+"""
+Python3 stack implementation that retrieves min/max elements of the stack in constant time
+"""
+from __future__ import annotations
+import math
+
+"""
+Data object for stack
+"""
+class StackData:
+    def __init__(self, current_value: float, min_value: float, max_value: float) -> None:
+        self.current_value = current_value
+        self.min_value = min_value
+        self.max_value = max_value
+
+"""
+Main stack implementation
+"""
+class MinMaxStack:
+    def __init__(self, max_stack_size: int = 10) -> None:
+        self.max_size = max_stack_size
+        self.stack = []
+
+    def push_value(self, value: float) -> bool:
+        """
+        >>> test_stack = MinMaxStack(3)
+        >>> test_stack.push_value(1)
+        True
+        >>> test_stack.push_value(2)
+        True
+        >>> test_stack.push_value(3)
+        True
+        >>> test_stack.push_value(4)
+        Traceback (most recent call last):
+            ...
+        Exception: Max stack size reached. Remove elements before adding new ones or increase stack size.
+
+        """
+
+        if len(self.stack) == self.max_size:
+            raise Exception("Max stack size reached. Remove elements before adding new ones or increase stack size.")
+
+        if len(self.stack) == 0:
+            self.stack.append(StackData(value, value, value))
+        else:
+            """Store min/max values with current value"""
+
+            new_min = min(self.stack[-1].min_value, value)
+            new_max = max(self.stack[-1].max_value, value)
+            self.stack.append(StackData(value, new_min, new_max))
+
+        return True
+
+    def pop_value(self) -> float:
+        """
+        >>> test_stack = MinMaxStack()
+        >>> test_stack.push_value(1)
+        True
+        >>> test_stack.push_value(2)
+        True
+        >>> test_stack.pop_value()
+        2
+        >>> test_stack.pop_value()
+        1
+        >>> test_stack.pop_value()
+        Stack is empty
+        -inf
+        """
+
+        if self.stack_is_valid():
+            return self.stack.pop().current_value
+
+        return -math.inf
+
+    def get_current_max(self) -> float:
+        """
+        test_stack = MinMaxStack(3)
+        >>> test_stack.push_value(-450.45)
+        True
+        >>> test_stack.push_value(450.45)
+        True
+        >>> test_stack.push_value(0)
+        True
+        >>> test_stack.get_current_max()
+        450.45
+        >>> test_stack.pop_value()
+        0
+        >>> test_stack.get_current_max()
+        450.45
+        >>> test_stack.pop_value()
+        450.45
+        >>> test_stack.get_current_max()
+        -450.45
+        >>> test_stack.pop_value()
+        -450.45
+        >>> test_stack.get_current_max()
+        Stack is empty
+        -inf
+        """
+        if self.stack_is_valid():
+            return self.stack[-1].max_value
+
+        return -math.inf
+
+    def get_current_min(self) -> float:
+        """
+        >>> test_stack = MinMaxStack(3)
+        >>> test_stack.push_value(123)
+        True
+        >>> test_stack.push_value(-123)
+        True
+        >>> test_stack.push_value(0)
+        True
+        >>> test_stack.get_current_min()
+        -123
+        >>> test_stack.pop_value()
+        0
+        >>> test_stack.get_current_min()
+        -123
+        >>> test_stack.pop_value()
+        -123
+        >>> test_stack.get_current_min()
+        123
+        >>> test_stack.pop_value()
+        123
+        >>> test_stack.get_current_min()
+        Stack is empty
+        -inf
+        """
+        if self.stack_is_valid():
+            return self.stack[-1].min_value
+
+        return -math.inf
+
+    def stack_is_valid(self) -> bool:
+        if len(self.stack) == 0:
+            print("Stack is empty")
+            return False
+
+        return True
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+    testmod()