Quicksort II

Another visualization of quicksort. Here, each row corresponds to the state of the array prior to recursing into each partition. The red lines represent the pivots.

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

body {
  padding: 10px 0;
}

svg {
  float: left;
}

.line {
  stroke: #000;
  stroke-linecap: round;
}

.line--pivot {
  stroke: #f00;
  stroke-width: 3px;
}

.line--inactive {
  stroke: #ddd;
}

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

var n = 200,
    array = d3.shuffle(d3.range(n)),
    levels = quicksort(array);

var margin = {top: 2, right: 20, bottom: 2, left: 20},
    width = 960 - margin.left - margin.right,
    height = 30 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
    .domain(d3.range(n))
    .rangePoints([0, width]);

var a = d3.scale.linear()
    .domain([0, n - 1])
    .range([-45, 45]);

var svg = d3.select("body").selectAll("svg")
    .data(levels)
  .enter().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 + ")");

svg.append("g")
    .attr("class", "line")
  .selectAll("line")
    .data(function(d) { return d; })
  .enter().append("line")
    .attr("transform", function(d, i) { return "translate(" + x(i) + "," + height + ")rotate(" + a(d == null ? i : d) + ")"; })
    .attr("class", function(d, i) { return d == null ? "line--inactive" : i in this.parentNode.__data__.pivots ? "line--pivot" : null; })
    .attr("y2", -height);

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

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;
  }

function recurse(left, right, depth) {
    var pivot = (left + right) >> 1;

if (!levels[depth]) levels[depth] = new Array(array.length), levels[depth].pivots = {};
    for (var i = left; i < right; ++i) levels[depth][i] = array[i];
    levels[depth].pivots[pivot] = 1;

pivot = partition(left, right, pivot);
    if (left < pivot - 1) recurse(left, pivot, depth + 1);
    if (pivot + 1 < right - 1) recurse(pivot + 1, right, depth + 1);
  }

if (array.length > 1) recurse(0, array.length, 0);
  return levels;
}

d3.select(self.frameElement).style("height", (height + margin.top + margin.bottom) * levels.length + 20 + "px");

</script>

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