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统计0到1亿中1出现的个数

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May 25, 2016 pm 05:12 PM

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function count_n($limit, $n) {
  if ($limit < $n) {
    return 0;
  }

  if ($limit == $n) {
    return 1;
  }

  $power = floor(log10($limit));
  $unit = pow(10, $power);
  $high = floor($limit / $unit);
  $low = $limit % $unit;

  return $high * $power * $unit / 10
      + (($high > $n)? $unit: (($high == $n)? 1 + $low: 0))
      + count_n($low, $n);
}

echo count_n(100000000, 1); // 80000001

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2. [代码]最初用 newLisp 写的函数

(define (count-n limit n)
  (if (< limit n) 0
    (= limit n) 1
    (letn (high (int ((string limit) 0))
           low (int (1 (string limit)))
           power (int (log limit 10)))
      (+ (count-n low n)
         (* high power (pow 10 (- power 1)))
         (if (> high n) (pow 10 power)
           (= high n) (+ 1 low)
           0)))))

(println (count-n 100000000 1))

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