From b0f4a25411f89e6d13a1f53f8cb4b0ba78d4c60b Mon Sep 17 00:00:00 2001
From: Laksha-python <laksha2552006@gmail.com>
Date: Fri, 28 Nov 2025 14:43:38 +0530
Subject: [PATCH 1/2] Improved space complexity to O(1) by using two pointers
 approach

---
 dynamic_programming/trapped_water.py | 34 ++++++++++++++--------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/dynamic_programming/trapped_water.py b/dynamic_programming/trapped_water.py
index 8bec9fac5fef..fb51621a5ac7 100644
--- a/dynamic_programming/trapped_water.py
+++ b/dynamic_programming/trapped_water.py
@@ -34,23 +34,23 @@ def trapped_rainwater(heights: tuple[int, ...]) -> int:
         return 0
     if any(h < 0 for h in heights):
         raise ValueError("No height can be negative")
-    length = len(heights)
-
-    left_max = [0] * length
-    left_max[0] = heights[0]
-    for i, height in enumerate(heights[1:], start=1):
-        left_max[i] = max(height, left_max[i - 1])
-
-    right_max = [0] * length
-    right_max[-1] = heights[-1]
-    for i in range(length - 2, -1, -1):
-        right_max[i] = max(heights[i], right_max[i + 1])
-
-    return sum(
-        min(left, right) - height
-        for left, right, height in zip(left_max, right_max, heights)
-    )
-
+    left,right=0,len(heights)-1
+    leftmax,rightmax=0,0
+    water=0
+    while left <right:
+        if heights[left] < heights[right]:
+            if heights[left] >= leftmax:
+                leftmax=heights[left]
+            else:
+                water+=leftmax - heights[left]
+            left+=1
+        else:
+            if heights[right] >= rightmax:
+                rightmax=heights[right]
+            else:
+                water+=rightmax - heights[right]
+            right-=1
+    return water
 
 if __name__ == "__main__":
     import doctest

From 3ab07d15b67a56f5722a26a3e0e90140083e9901 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Fri, 28 Nov 2025 09:18:59 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 dynamic_programming/trapped_water.py | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/dynamic_programming/trapped_water.py b/dynamic_programming/trapped_water.py
index fb51621a5ac7..5d950efd7264 100644
--- a/dynamic_programming/trapped_water.py
+++ b/dynamic_programming/trapped_water.py
@@ -34,24 +34,25 @@ def trapped_rainwater(heights: tuple[int, ...]) -> int:
         return 0
     if any(h < 0 for h in heights):
         raise ValueError("No height can be negative")
-    left,right=0,len(heights)-1
-    leftmax,rightmax=0,0
-    water=0
-    while left <right:
+    left, right = 0, len(heights) - 1
+    leftmax, rightmax = 0, 0
+    water = 0
+    while left < right:
         if heights[left] < heights[right]:
             if heights[left] >= leftmax:
-                leftmax=heights[left]
+                leftmax = heights[left]
             else:
-                water+=leftmax - heights[left]
-            left+=1
+                water += leftmax - heights[left]
+            left += 1
         else:
             if heights[right] >= rightmax:
-                rightmax=heights[right]
+                rightmax = heights[right]
             else:
-                water+=rightmax - heights[right]
-            right-=1
+                water += rightmax - heights[right]
+            right -= 1
     return water
 
+
 if __name__ == "__main__":
     import doctest