Function which calculates the largest area from a range of histogram points

largest-rectangle-from-histogram.js

/**
 * Largest Rectangle from Histogram
 *
 *  function which takes a range of histogram points,
 *  (array of natural numbers [or zero]), and returns the
 *  largest rectangle area that can fit inside of it.
 *
 * @param {Array<Number>} points The range of histogram points
 * @return {Number} The largest rectangle area
 *
 * @example
 *
 *  largestRectangleArea([3,1,4,2,5]); // => 6
 *  largestRectangleArea([2,3,4,1,7]); // => 7
 *  largestRectangleArea([7,0,5,4,5,4,0,11,12,8]); // => 24
 *  largestRectangleArea([]); // => 0
 *
 */
function largestRectangleArea(points) {
  return points.reduce(
    (currentSums, point) => {
      let len = point + 1;
      let nextSums = new Array(len);
      
      while (len--) {
        nextSums[len] = (currentSums[len] || 0) + len;
      }
      
      nextSums[0] = Math.max(...nextSums);
      
      return nextSums;
    },
    [0]
  )[0];
}

export default largestRectangleArea;