Twitter Interview Solution

gistfile1.java

/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int[] myIntArray = {2, 5, 1, 2, 3, 4, 7, 7, 6}; 
		System.out.println(calculateVolume(myIntArray));
	}
	
	public static int calculateVolume(int[] land) {
		
		int leftMax = 0;
		int rightMax = 0;
		int left = 0;
		int right = land.length - 1;
		int volume = 0;
		
		while(left < right) {
			if(land[left] > leftMax) {
				leftMax = land[left];
			}
			if(land[right] > rightMax) {
				rightMax = land[right];
			}
			if(leftMax >= rightMax) {
				volume += rightMax - land[right];
				right--;
			} else {
				volume += leftMax - land[left];
				left++;
			}
		}
		return volume;
	}
}

Whoops - found bug in my calculations - it should be 62 (not sure how I missed this during numerous manual verifications and my v1 impl :) )

unspoiled solution; I think mine works the same way as yours.
https://gist.github.com/Pranz/45eff77d201ef1e2dc61

This seems to work ...
https://gist.github.com/bourneagain/0cb90851106756746933

here is an alternate but simple nlog(n) solution
https://gist.github.com/isaiah-perumalla/105b72e6b99f69b599ec

just an F# solution for aestetic pleasure

let oneWayCapacity a =
    let mutable max = 0
    a |> List.map (fun e -> if e > max then max <- e; 0 else max - e)

let totalCapacity a =
    let aL = a |> oneWayCapacity
    let aR = a |> List.rev |> oneWayCapacity |> List.rev
    List.map2 min aL aR |> List.sum


let test a =
    a |> totalCapacity |>
    printfn "totalCapacity %A = %i" a

let () = 
    [1; 2; 1; 3; 5; 3; 1; 2; 4; 1] |> test
    [2; 5; 10; 7; 3; 8; 5; 2] |> test
    [2; 5; 1; 2; 3; 4; 7; 7; 6] |> test

https://gist.github.com/harry-tallbelt/cc236e710c9edf858853c118bc38c9ad