feat(work): add solutions for problems 42, 209, and 34

work/1/Hard/Array/42.trapping-rain-water.py

@@ -0,0 +1,56 @@
+"""
+42. Trapping Rain Water
+Difficulty: Hard
+https://leetcode.com/problems/trapping-rain-water/
+
+──────────────────────────────────────────────────
+
+Given n non-negative integers representing an elevation map where the
+width of each bar is 1, compute how much water it can trap after
+raining.
+
+
+
+Example 1:
+
+Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
+Output: 6
+Explanation: The above elevation map (black section) is represented
+by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain
+water (blue section) are being trapped.
+
+Example 2:
+
+Input: height = [4,2,0,3,2,5]
+Output: 9
+
+
+
+Constraints:
+
+        • n == height.length
+
+        • 1 <= n <= 2 * 10^4
+
+        • 0 <= height[i] <= 10^5
+"""
+
+
+class Solution:
+    def trap(self, height: list[int]) -> int:
+        left, right = 0, len(height) - 1
+        leftMax, rightMax = 0, 0
+        total = 0
+
+        while left < right:
+            leftMax = max(leftMax, height[left])
+            rightMax = max(rightMax, height[right])
+
+            if height[left] < height[right]:
+                total += leftMax - height[left]
+                left += 1
+            else:
+                total += rightMax - height[right]
+                right -= 1
+
+        return total