/r/dailyprogrammer problem #163 [hard + challenge]

163.js

function intersecting(a, b, c, d) {
  var intersection = [((a[0] * b[1] - a[1] * b[0]) * (c[0] - d[0]) - (a[0] - b[0]) * (c[0] * d[1] - c[1] * d[0])) /
    ((a[0] - b[0]) * (c[1] - d[1]) - (a[1] - b[1]) * (c[0] - d[0])),
    ((a[0] * b[1] - a[1] * b[0]) * (c[1] - d[1]) - (a[1] - b[1]) * (c[0] * d[1] - c[1] * d[0])) /
    ((a[0] - b[0]) * (c[1] - d[1]) - (a[1] - b[1]) * (c[0] - d[0]))];
  function between(a, b, c) {
    return c >= Math.min(a, b) && c <= Math.max(a, b);
  }
  if (between(a[0], b[0], intersection[0]) &&
      between(c[0], d[0], intersection[0]) &&
      between(a[1], b[1], intersection[1]) &&
      between(c[1], d[1], intersection[1])) {
    return intersection;
  }
  return false;
}

var Points = {
  a: [[-2.5, 0.5], [3.5, 0.5]],
  b: [[-2.23, 99.99], [-2.10, -56.23]],
  c: [[-1.23, 99.99], [-1.1, -56.23]],
  d: [[100.1, 1000.34], [2000.23, 2100.23]],
  e: [[1.5, -1], [1.5, 1]],
  f: [[2, 2], [3, 2]],
  g: [[2.5, 0.5], [2.5, 2]]
};

var intersectionSegments = [];
for (var c in Points) {
  var p = Points[c];
  var n = false;
  for (var c2 in Points) {
    if (c !== c2) {
      if (n) {
        var p2 = Points[c2];
        var i;
        if ((i = intersecting(p[0], p[1], p2[0], p2[1]))) {
          var m = [c, c2].sort().join(" ") + " at [" + i.join(", ") + "]";
          if (intersectionSegments.indexOf(m) === -1) {
            intersectionSegments.push(m);
          }
        }
      }
    } else {
      n = true;
    }
  }
}

console.log(intersectionSegments.join("\n"));