Merge pull request #28 from bt3gl-labs/add_on_solution

add an optimized solution

small-projects/other-puzzles/falling-rain-On.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python3
+
+'''
+We wish to compute the total amount of water that will be held by some
+topography when an infinite amount of evenly-distributed water is poured
+on it from above. The topography is represented by a sequence of integers
+describing the height of each unit-width section of terrain, from left to
+right. Your solution will return the total amount of width-times-height
+retained by the terrain. You may assume that heights are non-negative integers.
+
+Solution by bt3gl
+'''
+
+def _create_wall_array(size) -> list:
+    return [None for _ in range(size)]
+
+
+def _get_tallest_wall(wall1, wall2) -> int:
+    return (max(wall1, wall2))
+
+
+def _get_water_filling(left_wall, right_wall, middle) -> int:
+    return min(left_wall, right_wall) - middle
+
+
+def maxWater(arr) -> int:
+    """
+        Return the maximum water that can be stored
+        Input: arr (an array of positive integers)
+        Output: res (a positive integer)
+    """
+
+    res = 0
+    n = len(arr)
+    left_wall = _create_wall_array(n)
+    right_wall = _create_wall_array(n)
+    left_wall[0], right_wall[n - 1] = arr[0], arr[n - 1]
+
+    # Come from left
+    for i in range(1, n):
+        left_wall[i] = _get_tallest_wall(left_wall[i - 1], arr[i])
+
+    # Come from right
+    for i in range(n - 2, -1, -1):
+        right_wall[i] = _get_tallest_wall(right_wall[i + 1], arr[i]);
+
+    # Get water inside
+    for i in range(n):
+        res += _get_water_filling(left_wall[i], right_wall[i], arr[i])
+
+    return res
+
+
+
+# Test 1
+arr1 = [0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1]
+print(f'Solution for {arr1} is {maxWater(arr1)} (and should be 6)')
+
+# Test 2
+arr2 = [2, 0, 2]
+print(f'Solution for {arr2} is {maxWater(arr2)} (and should be 2)')
+
+# Test 3
+arr3 = [3, 0, 2, 0, 4]
+print(f'Solution for {arr3} is {maxWater(arr3)} (and should be 7)')
+
+# Test 4
+arr4 = [0, 0, 0, 0]
+print(f'Solution for {arr4} is {maxWater(arr4)} (and should be 0)')
+
+# Test 5
+arr5 = [5, 5, 5]
+print(f'Solution for {arr5} is {maxWater(arr5)} (and should be 0)')