Javascript to calculate seats in the Swedish parliament, The Riksdag, based on total number of votes and the results (percentage of votes) for an arbitrary number of parties.

calcRiksdagSeats.js

/**
 * Calculate number of seats in the Swedish parliament for an arbitrary number
 * of parties, from the total number of votes and each party's result as a
 * percentage of the total vote. Return an array containing the parties' respective
 * number of seats.
 *
 * The seats are distributed using a "Modified Sainte-Laguë method" algorithm where
 * the first divisor is 1.4.
 * 
 * In short, each party is given a "comparison value" based on the total number
 * of votes they received divided by 1.4. In each round, the party with the biggest
 * comparison value is awarded a seat and gets a new comparison number based on 
 * the next divisor in a series where 1.4 is followed by 3, 5, 7, 9, et c with
 * increments of 2. This continues until all seats have been distributed.
*/
function calcRiksdagSeats(numVotes, partyResults)
{
  var i, partyVotes, partyComps, partyDivs, partySeats, numSeats;
  
  partyVotes = [];
  partyComps = [];
  partySeats = [];
  partyDivs = [];
  numSeats = 0;
  
  // Set-up
  for (i=0; i<partyResults.length; i++) {
    partyVotes[i] = partyResults[i] * numVotes;
    partyComps[i] = partyVotes[i] / 1.4;
    partySeats[i] = 0;
    partyDivs[i] = 3;
    
    // Disqualify tiny parties (<4%)
    if (partyResults[i] < 0.04)
      partyComps[i] = 0;
  }
  
  // Loop over all seats and distribute them according to the
  // correct algorithm: For each seat, find the party with the
  // biggest comparison value, and award them the seat. Then
  // calculate that party's new comparison value by dividing it's
  // number of votes by the next divisor, starting at 3 and
  // incremented each time by 2.
  while (numSeats < 349) {
    var maxIdx, maxComp = 0;
    
    // Find maximum comparison value
    for (i=0; i<partyComps.length; i++) {
      if (partyComps[i] > maxComp) {
        maxComp = partyComps[i];
        maxIdx = i;
      }
    }
    
    // Add seat to biggest party after this round
    partySeats[maxIdx]++;
    numSeats++;
    
    // Prepare for next round by calculating new comparison value
    partyComps[maxIdx] = partyVotes[maxIdx] / partyDivs[maxIdx];
    partyDivs[maxIdx] += 2;
  }
  
  return partySeats;
}