Trapping Rain Water | Java implementation of the approach ; indices to traverse the array ; To store Left max and right max for two pointers left and right ; To store the total amount of rain water trapped ; We need check for minimum of left and right max for each element ; Add the difference between current value and right max at index r ; Update right max ; Update right pointer ; Add the difference between current value and left max at index l ; Update left max ; Update left pointer ; Driver code
import java . util . * ; class GFG { static int maxWater ( int [ ] arr , int n ) { int left = 0 ; int right = n - 1 ; int l_max = 0 ; int r_max = 0 ; int result = 0 ; while ( left <= right ) { if ( r_max <= l_max ) { result += Math . max ( 0 , r_max - arr [ right ] ) ; r_max = Math . max ( r_max , arr [ right ] ) ; right -= 1 ; } else { result += Math . max ( 0 , l_max - arr [ left ] ) ; l_max = Math . max ( l_max , arr [ left ] ) ; left += 1 ; } } return result ; } public static void main ( String [ ] args ) { int [ ] arr = { 0 , 1 , 0 , 2 , 1 , 0 , 1 , 3 , 2 , 1 , 2 , 1 } ; int n = arr . length ; System . out . print ( maxWater ( arr , n ) ) ; } }