lightoj--1294--Positive Negative Sign(水题,规律)
Time Limit: 2000MS | Memory Limit: 32768KB | 64bit IO Format: %lld & %llu |
Description
Given two integers: n and m and n is divisible by 2m, you have to write down the first n natural numbers in the following form. At first take first m integers and make their sign negative, then take next m integers and make their sign positive, the next m integers should have negative signs and continue this procedure until all the n integers have been assigned a sign. For example, let n be 12 and m be 3. Then we have
-1 -2 -3 +4 +5 +6 -7 -8 -9 +10 +11 +12
If n = 4 and m = 1, then we have
-1 +2 -3 +4
Now your task is to find the summation of the numbers considering their signs.
Input
Input starts with an integer T (≤ 10000), denoting the number of test cases.
Each case starts with a line containing two integers: n and m (2 ≤ n ≤ 109, 1 ≤ m). And you can assume that n is divisible by 2*m.
Output
For each case, print the case number and the summation.
Sample Input
2
12 3
4 1
Sample Output
Case 1: 18
Case 2: 2
Source
#include<stdio.h> #include<string.h> long long m,n; int main() { int t; scanf("%d",&t); int Case=1; while(t--) { long long sum=0; scanf("%lld%lld",&n,&m); printf("Case %d: ",Case++); sum=m*n/2;//就这麽一个简单的规律,超时好多次 printf("%lld\n",sum); } return 0; }