zcmu-1036: Shepherd（寻找特殊情况走出TLE的困境）

1036: Shepherd

Time Limit: 1 Sec  Memory Limit: 128 MB
Submit: 274  Solved: 72
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Description

Hehe keeps a flock of sheep, numbered from 1 to n and each with a weight wi. To keep the sheep healthy, he prepared some training for his sheep. Everytime he selects a pair of numbers (a,b), and chooses the sheep with number a, a+b, a+2b, … to get trained. For the distance between the sheepfold and the training site is too far, he needs to arrange a truck with appropriate loading capability to transport those sheep. So he wants to know the total weight of the sheep he selected each time, and he finds you to help him.

Input

There’re several test cases. For each case:
The first line contains a positive integer n (1≤n≤10^5)---the number of sheep Hehe keeps.
The second line contains n positive integer wi(1≤n≤10^9), separated by spaces, where the i-th number describes the weight of the i-th sheep.
The third line contains a positive integer q (1≤q≤10^5)---the number of training plans Hehe prepared.
Each following line contains integer parameters a and b (1≤a,b≤n)of the corresponding plan.

Output

For each plan (the same order in the input), print the total weight of sheep selected.

Sample Input

5 1 2 3 4 5 3 1 1 2 2 3 3

Sample Output

15 6 3

一次超时了，一次没用long long,贡献两次submit...

注释在代码里~ 

#include<stdio.h>
#include<string.h>
const int maxn = 1e5 + 5;
int c[maxn];
int main()
{
    int n,m,a,b,i;
    long long sum;//数据很大用LONGLONG
    while(scanf("%d",&n) != EOF)//多组输入
    {
        memset(c,0,sizeof(c));//清空数组
        long long total = 0;
        for(i = 1 ; i <= n;i++)
        {
            scanf("%d",&c[i]);
            total += c[i];
        }
        scanf("%d",&m);
        for(int i = 0 ;i < m;i++)
        {
            sum = 0;
            scanf("%d%d",&a,&b);
            if(a == 1 && b == 1)//把最耗时的一个情况单独考虑
                sum = total;
            else
            {
                for(int j = a;j <= n;j += b)
                    sum += c[j];
            }
            printf("%lld\n",sum);
        }
    }
    return 0;
}