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CF#277(Div.2)A.(找规律)_html/css_WEB-ITnose

时间:2021-07-01 10:21:17 帮助过:18人阅读

A. Calculating Function

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

题目链接: http://codeforces.com/contest/486/problem/A

For a positive integer n let's define a function f:

f(n)?=??-?1?+?2?-?3?+?..?+?(?-?1)nn

Your task is to calculate f(n) for a given integer n.

Input

The single line contains the positive integer n (1?≤?n?≤?1015).

Output

Print f(n) in a single line.

Sample test(s)

input

output

input

output

-3

Note

f(4)?=??-?1?+?2?-?3?+?4?=?2

f(5)?=??-?1?+?2?-?3?+?4?-?5?=??-?3



解题思路:

给你n,求f(n) 。这是一道规律题,首先确定不能暴力求解,因为n实在太大,暴力必超时。同时也开不了那么大的数组来暴力。

提笔简单算了几个,发现f(1) = -1 , f(2) = 1, f(3) = -2, f(4) = 2, f(5) = -3, f(6) = 3··········这样规律就看出来了,两个数一组,n/2如果为偶数那么符号为正,奇数符号为负。并且如果n/2为奇数的话,我们向上取整,即为n / 2 + 1

最后,中间值什么的都开成long long。

完整代码:

#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std;#pragma comment(linker, "/STACK:102400000,102400000")typedef long long LL;typedef double DB;typedef unsigned uint;typedef unsigned long long uLL;/** Constant List .. **/ //{const int MOD = int(1e9)+7;const int INF = 0x3f3f3f3f;const LL INFF = 0x3f3f3f3f3f3f3f3fLL;const DB EPS = 1e-9;const DB OO = 1e20;const DB PI = acos(-1.0); //M_PI;int main(){    #ifdef DoubleQ    freopen("in.txt","r",stdin);    #endif    LL n;    while(~scanf("%lld",&n))    {        LL c = n / 2;        if(n % 2 != 0)        {            c += 1;            printf("-");        }        printf("%lld\n" , c);    }}

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