Add 'Daily Temperatures'

Author: nickolashkraus

README.md

@@ -22,6 +22,8 @@ A collection of LeetCode solutions
 
 [Contains Duplicate](./src/contains_duplicate.py)
 
+[Daily Temperatures](./src/daily_temperatures.py)
+
 [Find Median from Data Stream](./src/find_median_from_data_stream.py)
 
 [Flood Fill](./src/flood_fill.py)

src/daily_temperatures.py

@@ -0,0 +1,53 @@
+"""
+739. Daily Temperatures
+
+https://leetcode.com/problems/daily-temperatures
+
+NOTES
+  * Traverse the array from the right and use a monotonically decreasing stack.
+
+Stacks vs. Queues
+-----------------
+A monotonic stack and a monotonic queue are similar data structures that
+maintain elements in a monotonic order (either strictly decreasing or strictly
+increasing), but they differ in their operations and use cases.
+
+  Monotonic Stack
+    * Elements are added/removed from the same end (LIFO - Last In, First Out).
+    * Uses push and pop operations.
+    * When adding a new element, pops existing elements that violate the
+      monotonic property.
+    * Typically used to find the "next greater/smaller element" or to solve
+      problems involving ranges where elements dominate others.
+
+  Monotonic Queue
+    * Elements are added at one end and removed from the other (FIFO - First
+      In, First Out).
+    * Uses enqueue (append) at one end and dequeue (popleft) from the other.
+    * When adding a new element, removes existing elements that violate the
+      monotonic property.
+    * Often used for sliding window problems to efficiently track
+      maximum/minimum values within the window.
+
+In Python, a deque can be used for both stacks and queues, however, it is
+important to differentiate when/how each data structure should be used:
+    * Stack: push, pop
+    * Queue: append, popleft
+"""
+
+from collections import deque
+
+
+class Solution:
+    def dailyTemperatures(self, temperatures: list[int]) -> list[int]:
+        stack: deque[int] = deque()
+        ans: list[int] = [0] * len(temperatures)
+
+        for i in reversed(range(len(temperatures))):
+            while stack and temperatures[i] >= temperatures[stack[-1]]:
+                stack.pop()
+            if stack and temperatures[i] < temperatures[stack[-1]]:
+                ans[i] = stack[-1] - i
+            stack.append(i)
+
+        return ans

tests/test_daily_temperatures.py

@@ -0,0 +1,30 @@
+"""
+739. Daily Temperatures
+
+https://leetcode.com/problems/daily-temperatures
+"""
+
+from unittest import TestCase
+
+from src.daily_temperatures import Solution
+
+
+class TestSolution(TestCase):
+    def test_1(self):
+        exp = [1, 1, 4, 2, 1, 1, 0, 0]
+        assert Solution().dailyTemperatures([73, 74, 75, 71, 69, 72, 76, 73]) == exp
+
+    def test_2(self):
+        exp = [1, 1, 1, 0]
+        assert Solution().dailyTemperatures([30, 40, 50, 60]) == exp
+
+    def test_3(self):
+        exp = [1, 1, 0]
+        assert Solution().dailyTemperatures([30, 60, 90]) == exp
+
+    def test_4(self):
+        exp = [8, 1, 5, 4, 3, 2, 1, 1, 0, 0]
+        assert (
+            Solution().dailyTemperatures([89, 62, 70, 58, 47, 47, 46, 76, 100, 70])
+            == exp
+        )