Quicksort V

A visualization of quicksort. Each row represents the state of the array after a single swap operation.

See also sortvis.org by Aldo Cortesi and sorting visualizations by Jason Davies.

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

body {
  background: #000;
}

.line {
  fill: none;
  stroke: #000;
  stroke-width: 6px;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.line-halo {
  stroke-linecap: butt;
  stroke-width: 8px;
}

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

var n = 100,
    array = d3.shuffle(d3.range(n)),
    swaps = quicksort(array.slice()),
    elements = array.map(function(v, i) { return {value: v, indexes: [{time: 0, index: i}]}; });

var color = d3.scale.cubehelix()
    .domain([0, n / 2, n - 1])
    .range([d3.hsl(-40, 1, .4), d3.hsl(60, 1, 1), d3.hsl(160, 1, .4)]);

swaps.forEach(function(s, t) {
  var i = s[0], j = s[1];
  elements[i].indexes.push({time: t + 1, index: j});
  elements[j].indexes.push({time: t + 1, index: i});
  t = elements[i], elements[i] = elements[j], elements[j] = t;
});

elements.forEach(function(e) {
  e.indexes.push({time: swaps.length + 1, index: e.indexes[e.indexes.length - 1].index});
});

var margin = {top: 20, right: 20, bottom: 20, left: 20},
    rowHeight = 20,
    strokeWidth = 6,
    width = 960 - margin.left - margin.right,
    height = (swaps.length + .5) * rowHeight;

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

var lineStraight = d3.svg.line()
    .interpolate(interpolateLineStraight)
    .x(function(d) { return x(d.index); })
    .y(function(d) { return rowHeight * d.time; });

var lineSwap = d3.svg.line()
    .interpolate(interpolateLineSwap)
    .x(function(d) { return x(d.index); })
    .y(function(d) { return rowHeight * d.time; });

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 + ")");

svg.append("g")
    .attr("class", "line line--straight")
  .selectAll("path")
    .data(elements)
  .enter().append("path")
    .style("stroke", function(d) { return color(d.value); })
    .attr("d", function(d) { return lineStraight(d.indexes); });

svg.append("g")
    .attr("class", "line line--swap")
  .selectAll("path")
    .data(d3.merge(elements
      .map(function(e) {
        var swaps = d3.pairs(e.indexes).slice(0, -1);
        swaps.forEach(function(s) { s.value = e.value; });
        return swaps;
      })))
  .enter().append("path")
    .style("stroke", function(d) { return color(d.value); })
    .attr("d", function(d) { return lineSwap(d); })
  .select(function() { return this.parentNode.insertBefore(this.cloneNode(false), this); })
    .attr("class", "line-halo")
    .style("stroke", null)
    .style("stroke-dasharray", function() {
      var l = this.getTotalLength();
      return "0," + strokeWidth / 2 + "," + (l - strokeWidth) + "," + strokeWidth / 2;
    });

function interpolateLineStraight(points) {
  var p0 = points[0],
      x0 = p0[0],
      y0 = p0[1],
      path = [p0];
  for (var i = 1, n = points.length, p1, x1, y1; i < n; ++i) {
    p1 = points[i];
    x1 = p1[0];
    y1 = p1[1];
    path.push("V", y1 - rowHeight / 2, "M", p1);
    x0 = x1;
    y0 = y1;
  }
  return path.join("");
}

function interpolateLineSwap(points) {
  var p0 = points[0],
      x0 = p0[0],
      y0 = p0[1],
      path = [p0];
  for (var i = 1, n = points.length, p1, x1, y1; i < n; ++i) {
    p1 = points[i];
    x1 = p1[0];
    y1 = p1[1];
    path.push("M", x0, ",", y1 - rowHeight / 2, "L", p1);
    x0 = x1;
    y0 = y1;
  }
  return path.join("");
}

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

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) {
    if (i === j) return;
    var t = array[i];
    array[i] = array[j];
    array[j] = t;
    swaps.push([i, j]);
  }

function recurse(left, right) {
    if (left < right - 1) {
      var pivot = partition(left, right, (left + right) >> 1);
      recurse(left, pivot);
      recurse(pivot + 1, right);
    }
  }

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

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

</script>

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