Trapping rain water solution - leetcode 42

dp/Trapping Rain Water/trapping_rain_water_solution.py

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+# Optimal Solution - O(1) solution
+class Solution:
+    def trap(self, height: List[int]) -> int:
+
+        if not height: return 0
+
+        l, r = 0, len(height) - 1
+        leftMax, rightMax = height[l], height[r]
+        res = 0
+
+        while l < r:
+            if leftMax < rightMax:
+                l += 1
+                leftMax = max(leftMax, height[l])
+                res += leftMax - height[l]
+            else:
+                r -= 1
+                rightMax = max(rightMax, height[r])
+                res += rightMax - height[r]
+        return res
+
+# Try O(n) solution using arrays as memory