数据结构与算法分析C语言版-第10章289页：将递归算法改为时间复杂度为O(n)的非递归算法

#include <iostream>
using namespace ::std;

double Eval( int N )  //递归方法
{
    int i;
    double Sum;

    if( N == 0 )
        return 1.0;
    else
    {
        Sum = 0.0;
        for( i = 0; i < N; i++ )
            Sum += Eval( i );
        return 2.0 * Sum / N + N;
    }
}

double iEval( int N ) //非递归方法
{
    int i;
    double Sum;
	double left, right;

    if( N == 0 )
        return 1.0;  //C0 = 1.0;
	else if( N == 1 )
		return 3.0;  //C1 = 3.0;
    else
    {
        Sum = 0.0;

		left = 3.0;  //左子节点
		right = 1;   //右子节点和
        for( i = 2; i <= N; i++ )
		{
			Sum = 2.0 * (left + right) / i + i;
			right = left + right; 
			left = Sum;
		}
        return Sum;
    }
}

int main()
{
	printf( "%f\n", Eval( 25 ) );
	printf( "%f\n", iEval( 25 ) );
	system( "PAUSE");
	return 0;
}