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#!/bin/env python
"""
===============================================================================
#
# FILE: ch-2.py
#
# USAGE: ./ch-2.py
#
# DESCRIPTION: Perl Weekly Challenge Task 2
# https://perlweeklychallenge.org/blog/perl-weekly-challenge-079/
# Trapper Rain Water
#
# AUTHOR: Lubos Kolouch
#==============================================================================
"""
def trapWater(arr):
n = len(arr)
left = [0]*n
right = [0]*n
water = 0
left[0] = arr[0]
for i in range(1, len(arr)):
left[i] = max(left[i-1], arr[i])
right[n-1] = arr[n-1]
for i in range(n-2, -1, -1):
right[i] = max(right[i + 1], arr[i])
for i in range(0, n):
water += min(left[i], right[i]) - arr[i]
return water
assert trapWater([2, 1, 4, 1, 2, 5]) == 6
assert trapWater([3, 1, 3, 1, 1, 5]) == 6
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