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Trapping_rain_water.java
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Trapping_rain_water.java
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/* Given n non-negative integers representing an elevation map where the
width of each bar is 1, compute how much water it can trap after raining. */
import java.io.*;
import java.util.*;
class Trapping_rain_water {
static int trap(int arr[]) {
// Your code here
int n = arr.length;
if (n == 0)
return 0;
int left[] = new int[n];
int right[] = new int[n];
// Initialize result
int water = 0;
// Fill left array
left[0] = arr[0];
for (int i = 1; i < n; i++)
left[i] = Math.max(left[i - 1], arr[i]);
// Fill right array
right[n - 1] = arr[n - 1];
// Find max
for (int i = n - 2; i >= 0; i--)
right[i] = Math.max(right[i + 1], arr[i]);
// Find min
for (int i = 0; i < n; i++)
water += Math.min(left[i], right[i]) - arr[i];
// return the answer
return water;
}
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter number of elements: ");
int n = sc.nextInt();
int arr[] = new int[n];
System.out.println("Enter the elements: ");
for (int i = 0; i < n; i++)
arr[i] = sc.nextInt();
System.out.println("Water it can trap is: " + trap(arr));
}
}
/*
Time Complexity: O(n)
Space Complexity: O(n)
Example 1:
Input:
Enter number of elements:
12
Enter the elements:
0 1 0 2 1 0 1 3 2 1 2 1
Output:
Water it can trap is: 6
Example 2:
Input:
Enter number of elements:
5
Enter the elements:
1 4 2 0 1
Output:
Water it can trap is: 1
*/