分发红包的算法

function distribute($total, $num) {
  $avg = $total / $num;
  $r = array_fill(0, $num, $avg);

  for($i=0; $i<$num; $i+=2) {
    $t = rand(1, $avg * 100) / 100;
    $r[$i] -= $t;
    if($r[$i] <= 0) $r[$i] = 0.01;
    $r[$i+1] += $t;
  }
  $r[$num-1] = $total - array_sum(array_slice($r, 0, -1));
  return $r;
}