找规律计算 series_sum

Author: uuk020

series_sum/series_sum.php

@@ -0,0 +1,36 @@
+<?php
+/**
+ * 规律计算题
+ * Your task is to write a function which returns the sum of following series upto nth term(parameter).
+ * Series: 1 + 1/4 + 1/7 + 1/10 + 1/13 + 1/16 +...
+ * You need to round the answer to 2 decimal places and return it as String.
+ * If the given value is 0 then it should return 0.00
+ * You will only be given Natural Numbers as arguments.
+ */
+function series_sum($n)
+{
+  // Your code here
+  $offset = 1;
+  if (!is_int($n)) {
+      return '$n is not int';
+  }
+  if ($n === 0) {
+      return 0.00;
+  }
+  for ($i = 0; $i < $n; $i++) {
+      $sum += 1 / $offset;
+      // 规律: 4 7 10..每次除于的数都是上个数+3
+      $offset += 3;
+  }
+  return round($sum, 2);
+}
+
+function series_sum_clever($n)
+{
+  $sum = 0;
+  for($i=0; $i<$n; $i++) {
+    //结合循环$i 计算每次要除于的数.为$i的值*3+1得出
+     $sum += 1/(1+3*$i);
+  }
+  return round($sum,2);
+}