gistfile1.js

/**
 * @param lo The closest previous input below the current input
 * @param hi The closest previous input above the current input
 * @param loPos The position of lo
 * @param hiPos The position of hi
 * @param input The current input
 * @return The optimal position for input
 */
function optimalGuess(lo, hi, loPos, hiPos, input) {
  // Track the best values
  var maxGapAmount = 0, maxMinGapPerNum = 0, optimalPos = 0;
  // Test each possible position
  for (var i = loPos+1; i < hiPos; i++) {
    // Calculate the gaps
    var posAbove = hiPos - i - 1, posBelow = i - loPos - 1;
    var gapAmount = (posAbove ? (hi - input) : 0) + (posBelow ? (input - lo) : 0);
    var gapPerNumAbove = (posAbove ? (hi - input) / posAbove : 0);
    var gapPerNumBelow = (posBelow ? (input - lo) / posBelow : 0);
    var minGapPerNum = Math.min(gapPerNumAbove, gapPerNumBelow);
    // If we have the same size gap, optimize for the largest minimum gap per number.
    // In other words we don't want to cram a bunch of numbers into a small gap on one side and have a big gap on the other side.
    if (maxGapAmount < gapAmount || (maxGapAmount == gapAmount && maxMinGapPerNum < minGapPerNum)) {
      maxGapAmount = gapAmount;
      maxMinGapPerNum = minGapPerNum;
      optimalPos = i;
    }
  }
  return optimalPos;
}