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{Rainwater Collector}

The Question

You're an industrious programmer that lives off the grid. The local well that you use to fetch water has gone dry, so you've decided to collect rain water to filter. However, your collection device isn't flat.

PROBLEM: Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water your collection device is able to trap after raining.

Example

EXAMPLE: Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.

Tests to Run

// vol = 7
var a = [0,0,1,2,4,3,2,5,0,0,2,1]
console.log('collection device "a" can hold', totalVol(a))
 
// vol = 6
var b = [0,1,0,2,1,0,1,3,2,1,2,1]
console.log('collection device "b" can hold', totalVol(b))
 
// vol = 12
var c =[0,3,0,1,0,0,0,1,0,2]
console.log('collection device "c" can hold', totalVol(c))
 
// vol = 8
var d = [0,1,0,3,5,0,0,0,2,0,1]
console.log('collection device "d" can hold', totalVol(d))
 
// vol = 38
var e = [0,5,3,2,8,8,1,1,2,4,3,3,7,1,2,4,3,2]
console.log('collection device "e" can hold', totalVol(e))