C#练习题答案: 序列的总和[硬核版]【难度：2级】--景越C#经典编程题库,1000道C#基础练习题等你来挑战

序列的总和[硬核版]【难度:2级】:

答案1:

using System;
public static class Kata
{
  public static long SequenceSum(long start, long end, long step)
  {
    if (Math.Sign(end-start) != Math.Sign(step))
      return 0;

    end -= (end-start)%step;
    return (start+end)*(1+(end-start)/step)/2;
  }
}​

答案2:

public static class Kata
{
  public static long SequenceSum(long s, long e, long d)
  {
    var n = (e-s) / d + 1;
    return (e*d <= s*d) ? 0 : n*s + n*(n-1)*d/2;
  }
}​

答案3:

public static class Kata
{
    public static long SequenceSum(long start, long end, long step)
    {
        if (step == 0 || step > 0 &amp;&amp; end <= start || step < 0 &amp;&amp; start <= end) return 0;
        var count = (end - start) / step + 1;
        return count * start + step *count* (count - 1) / 2;
    }
}​

答案4:

using System;
public static class Kata
{
  public static long SequenceSum(long start, long end, long step)
  {
      if((end<start &amp;&amp; step>0) || (end>start &amp;&amp; step<0) || end==start)
        return 0;
      long count = ((end - start) / step) + 1;
      return ((count - 1) * (step) + 2 * start) * count / 2;
  }
}​

答案5:

using System;
public static class Kata
{
  public static long SequenceSum(long start, long end, long step)
  {
    if (start >= end &amp;&amp; step > 0 || start <= end &amp;&amp; step < 0) return 0;
    long last = (end - start) % step == 0 ? end : end - (end - start) % step;
    long n = (last - start) / step + 1;
    long sum = (long)((start + last) / 2.0 * n);
    return sum;
  }
}​

答案6:

using System;

public static class Kata {
    public static long SequenceSum( long start, long end, long step ) {
        if ( start >= end && step > 0 ) {
            return 0;
        }
        if ( start <= end &amp;&amp; step < 0 ) {
            return 0;
        }
        long n = Math.Abs( ( end - start )/step ) + 1;
        var a1 = start;
        var an = a1 + step*( n - 1 );
        var sum = ( ( a1 + an )/2.0 )*n;
        return ( long ) sum;
    }
}​

答案7:

using System;
public static class Kata
{
  public static long SequenceSum(long start, long end, long step)
  {
     long sum = 0;
             if ((start > end &amp;&amp; step > 0) || (end > start &amp;&amp; step < 0) || start == end) 
                return 0;

            long n = (end - start + step) / step;
            long end1 = start + step * (n - 1);
            sum = (start + end1) * n / 2;
            return sum;
  }
}​

答案8:

using System;
using System.Linq;

public static class Kata
{
  public static long SequenceSum(long start, long end, long step)
  {
     if (step > 0 && start>=end) return 0L;
     if (step < 0 &amp;&amp; start<=end) return 0L;
     
     long a = (end-start)/step;
     return (a+1)*start+step*a*(a+1)/2L;
  }
}​

答案9:

using System;
public static class Kata
{
  public static long SequenceSum(long start, long end, long step)
  {
    if(end<start&amp;&amp;step>0 || end>start&amp;&amp;step<0 || end==start)
      return 0;
    long n=(end-start)/step+1;
    return n*(2*start+(n-1)*step)/2;
  }
}​

答案10:

using static System.Math;

public static class Kata
{
  public static long SequenceSum(decimal start, decimal end, decimal step)
  {
    if ((start >= end &amp;&amp; step > 0) || (start <= end &amp;&amp; step < 0))
      return 0;
    end = (end - start) - ((end - start) % step);
    var count = Ceiling((end + Sign(step)) / step);
    var prefix = Max(1, count) * start;    
    var suffix = end * (end + step) / (step * 2);
    return (long)(prefix + suffix);
  }
}​