You are an engineer in government water management. After many days of heavy rain there is a great risk of floods in populated regions. You are tasked with a quick calculation of water retention capacity of terrain.

You have access to terrain data as an array of heights, e.g.

[3, 1, 4, 2, 3, 1]

represents terrain of shape

HEIGHTS:
 3 1 4 2 3 1

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 A B C D E F

The terrain data contains just the highlands. At the left and the right, the terrain continues with plains leading to populated regions, so what is not retained in provided data, spills out.

The terrain from example has the capacity of 3. Two capacity units retains in column B and one unit retains column D. The column F has no capacity, for it is at the edge and we assume continuing plains.

The retention capacity visualized

CAPACITY:
 0 2 0 1 0 0

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 A B C D E F

Tasks

1. Create program in JavaScript or TypeScript which will perform calculation of such retention capacity. Deliver it as project with a README.md describing how to use the program. You can send a .zip file or provide link to public repository on GitHub, project on CodeSandbox, etc.
2. Compute retention capacity of following terrain:

[51,94,91,57,82,6,94,4,0,71,10,12,32,11,49,8,67,72,1,36,33,35,37,3,2,6,57,4,4,57,32,5,25,45,16,25,6,55,55,2,10,84,2,50,48,0,83,24,14,4,5,5,93,0,20,73,99,0,3,80,30,4,0,59,10,29,92,35,79,90,33,20,79,5,2,31,42,83,16,6,82,39,32,3,1,47,6,3,56,70,32,64,25,82,1,70,53,5,6,70,94,83,46,47,57,30,64,85,4,99,46,0,74,56,3,59,10,52,85,37,6,3,2,68,32,11,76,89,43,35,11,64,8,5,62,1,47,0,1,1,49,25,27,38,78,80,3,6,25,2,98,0,1,93,97,9,20,87,43,56,7,33,46,17,75,85,5,1,39,81,84,27,20,0,4,6,88,0,27,87,23,1,71,37,32,59,20,55,26,58,89,2,0,6,3,32,1,0,79,9]