Quicksort

<!DOCTYPE html>
<meta charset="utf-8">
<body>
<style>

line {
  stroke: #000;
  stroke-width: 1.5px;
}

</style>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

var margin = {top: 230, right: 30, bottom: 230, left: 30},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var n = 240,
    index = d3.range(n),
    data = shuffle(index.slice());

var x = d3.scale.ordinal().domain(index).rangePoints([0, width]),
    a = d3.scale.linear().domain([0, n - 1]).range([-Math.PI / 4, Math.PI / 4]);

var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + (margin.top + height) + ")");

// Fisher–Yates shuffle
function shuffle(array) {
  var i = array.length, j, t;
  while (--i > 0) {
    j = ~~(Math.random() * (i + 1));
    t = array[j];
    array[j] = array[i];
    array[i] = t;
  }
  return array;
}

function quicksort(array) {
  var actions = [];

function partition(left, right, pivot) {
    var v = array[pivot];
    swap(pivot, --right);
    for (var i = left; i < right; ++i) if (array[i] <= v) swap(i, left++);
    swap(left, right);
    return left;
  }

function swap(i, j) {
    var t = array[i];
    array[i] = array[j];
    array[j] = t;
    actions.push({type: "swap", i: i, j: j});
  }

recurse(0, array.length);
  return actions;
}

var actions = quicksort(data).reverse();

setInterval(function step() {
  var action = actions.pop();
  if (action) switch (action.type) {
    case "partition": {
      line.style("stroke", function(d, i) { return i == action.pivot ? "red" : null; });
      step();
      break;
    }
    case "swap": {
      var t = line[0][action.i];
      line[0][action.i] = line[0][action.j];
      line[0][action.j] = t;
      line.attr("transform", function(d, i) { return "translate(" + x(i) + ")"; });
      break;
    }
  }
}, 20);

</script>

https://d3js.org/d3.v3.min.js