[解题报告]10783 - Odd Sum

  Odd Sum 

Given a range [a, b], you are to find the summation of all the odd integers in this range. For example, the summation of all the odd integers in the range [3, 9] is 3 + 5 + 7 + 9 = 24.

Input 

There can be at multiple test cases. The first line of input gives you the number of test cases, T ( 1T100). Then T test cases follow. Each test case consists of 2 integers a and b ( 0ab100) in two separate lines.

Output 

For each test case you are to print one line of output - the serial number of the test case followed by the summation of the odd integers in the range [a, b].

Sample Input 

2
1
5
3
5

Sample Output 

Case 1: 9
Case 2: 8

 

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Miguel Revilla 2004-12-02

 

 

 

将

a+(a+2)+(a+4)+…+b

转换为
(1+3+5+…+b)-(1+3+5+…+(a-2))=((b+1)/2)^2 – ((a-1)/2)^2

 

 

#include<stdio.h>
int main()
{
  int T;
  int a,b,i;
  while(scanf("%d",&T)!=EOF)
  {
    for(i=1;i<=T;i++)
    {
      scanf("%d%d",&a,&b);
      if(!(a%2)) a++;
      if(!(b%2)) b--;
      printf("Case %d: %d\n",i,(b+1)/2*(b+1)/2-(a-1)/2*(a-1)/2);
    }
  }
  return 0;
}