gistfile1.js

var towerSolver = function(blocks) {
  var result = 0;
  var wallHeight = 0;
  var underWater = [];

  for (var i = 0; i < blocks.length; i++) {
    if (blocks[i] >= wallHeight || i === blocks.length - 1) {
      var smallestWall = Math.min(blocks[i], wallHeight);
      wallHeight = blocks[i];

      while (underWater.length > 0) {
        result += (smallestWall - underWater.pop());
      }
    } else {
      underWater.push(blocks[i]);
    }
  }

  return result;
}