Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

<script id="jsbin-javascript">
function rainWater(buildHeight) {
	var length = buildHeight.length,
  		waterQty = 0;
  console.log
	//array to store largest building height to the left of current building
  var leftMax = [];

  //array to store largest building height to the right of current building
  var rightMax = [];

  leftMax[0] = buildHeight[0];
  rightMax[length-1] = buildHeight[length-1];

  for(var i=1; i<length; i++) {
  	leftMax[i] = Math.max(leftMax[i-1], buildHeight[i]);
  }

  for(var i = length-2; i>=0; i--) {
  	rightMax[i] = Math.max(rightMax[i+1], buildHeight[i]);
  }

  for(var i=1; i<length; i++) {
  	waterQty = waterQty + (Math.min(leftMax[i], rightMax[i])) - buildHeight[i];
  }

	return waterQty;
}

var input = [3,0,0,2,0,4];
console.log(rainWater(input));
</script>


<script id="jsbin-source-javascript" type="text/javascript">function rainWater(buildHeight) {
	var length = buildHeight.length,
  		waterQty = 0;
  console.log
	//array to store largest building height to the left of current building
  var leftMax = [];

  //array to store largest building height to the right of current building
  var rightMax = [];

  leftMax[0] = buildHeight[0];
  rightMax[length-1] = buildHeight[length-1];

  for(var i=1; i<length; i++) {
  	leftMax[i] = Math.max(leftMax[i-1], buildHeight[i]);
  }

  for(var i = length-2; i>=0; i--) {
  	rightMax[i] = Math.max(rightMax[i+1], buildHeight[i]);
  }

  for(var i=1; i<length; i++) {
  	waterQty = waterQty + (Math.min(leftMax[i], rightMax[i])) - buildHeight[i];
  }

	return waterQty;
}

var input = [3,0,0,2,0,4];
console.log(rainWater(input));</script></body>
</html>