算法学习之求数列和

Question：

Given a sequence of n integers, , and a small positive integer k, write an algorithm to compute

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技巧：

1，应用Honer's Rule，进行累积运算，减少循环层次；

2，应用bitwise shifts，将乘二变成左移一位；

long SeriesSum(int a[], unsigned n, unsigned k){    long sum = a[n-1];    for (int i = n-2; i >=0; --i)        sum = (sum << k) + a[i];    return sum;}

测试代码：

#include <windows.h>   // for GetTickCount()#include <iostream>#include <cstdlib>    // for rand() and srand()#include <ctime>      // for time()long SeriesSum(int a[], unsigned n, unsigned k);int main(){std::srand(GetTickCount());    // std::srand(time(0));unsigned max = 100;int n = 5;int* array = new int[n]{};for (int i = 0; i < n; i++)array[i] = std::rand() % max;int k = 3;long sum = SeriesSum(array, n, k);return 1;}