student_question.js

student_question.js

'use strict';

/**
$node perfs.js
___________________________________________________[Bench] Generating table (size=1600000) took: 593ms
sum=816028274.8700228
avg=510.01767179376424
___________________________________________________[Bench] Calculating sum took: 78ms
___________________________________________________[Bench] Sort users by rank DESC took: 2702ms
Best score user(id=1322940, score=1010, rank=0)
Lowest score user(id=1495965, score=10, rank=0)
___________________________________________________[Bench] Update rank took: 227ms
___________________________________________________[Bench] Total runtime took: 3602ms
___________________________________________________[Bench] (bonus) sort users by id ASC took: 2596ms
First user(id=1057231, score=1010, rank=1)
Last user(id=1495965, score=10, rank=1599999)
 */

var _ = require('lodash');
var TABLE_SIZE = 1600000;

var table, sum, avg;

bench('Total runtime', function () {
  bench('Generating table (size=' + TABLE_SIZE + ')', function () {
    // first generate a dummy table
    table = _.range(0, TABLE_SIZE).map(function (v) {
      // model : [user_id, score, rank]
      return [v, Math.round(1000 + Math.random() * 100000) / 100, 0]; // 0 because I don't know the current gamer rank
    });
  });

  bench('Calculating sum', function () {
    sum = table.reduce(function (a, b) {
      return a + b[1];
    }, 0);
    avg = sum / table.length;
    console.log('sum=%s', sum);
    console.log('avg=%s', avg);
  });

  bench('Sort users by rank DESC', function () {
    // .sort (mutable, edit in place) took 2644ms
    // .sortBy (immutable, returns a copy) took 7747ms
    table.sort(function (a, b) {
      return b[1] - a[1];
    });
  });

  print('Best score', _.first(table));
  print('Lowest score', _.last(table));

  bench('Update rank', function () {
    // still mutable
    table.forEach(function (v, rank) {
      // update rank (because rank == element index)
      v[2] = rank;
    });
  });
});

bench('(bonus) sort users by id ASC', function () {
  // still mutable
  table.sort(function (a, b) {
    return a[0] - b[0];
  });
});

print('First', _.find(table, {
  2: 1
}));

print('Last', _.find(table, {
  2: TABLE_SIZE - 1
}));

function print(prefix, v) {
  console.log('%s user(id=%s, score=%s, rank=%s)', prefix, v[0], v[1], v[2]);
}

function bench(label, f) {
  label = '___________________________________________________[Bench] ' + label + ' took';
  console.time(label);
  f();
  console.timeEnd(label);
}