# Uva-10014-simple Calculations (Classic math derivation!!) ）

Source: Internet
Author: User

UVA-10014

Simple calculations
 Time Limit: 3000MS Memory Limit: Unknown 64bit IO Format: %lld &%llu

Submit Status

Description

 Simple calculations
The problem

There is a sequence of n+2 elements a0, A1,..., An+1 (n <=, -1000 <= AI 1000). It is known this ai = (ai–1 + ai+1)/2–ci for each i=1, 2, ..., N. You are given A0, an+1, C1, ..., CN. Write A program which calculates A1.

The Input

The first line was the number of test cases, followed by a blank line.

For each test case, the first line of a input file contains an integer n. The next lines consist of numbers a0 and an+1 each have a digits after decimal point, and the next n lines contain Numbers CI (also with the digits after decimal point), one number per line.

Each test case is separated by a.

The Output

For each test case, the output file should contain A1 in the same format as A0 and an+1.

Print a blank line between the outputs for the consecutive test cases.

Sample Input
`1`
`1`
`50.50`
`25.50`
`10.15`
Sample Output
`27.85`

Source

Root:: Prominent problemsetters:: Alex Gevak
Root:: Competitive programming 3:the New Lower Bound of programming contests (Steven & Felix Halim):: Mathematics: : Ad Hoc Mathematics problems:: Finding Pattern or Formula, easier
Root:: Competitive programming 2:this increases the lower bound of programming contests. Again (Steven & Felix Halim):: Mathematics:: Ad Hoc Mathematics problems:: Finding Pattern or Formula
Root:: AOAPC i:beginning algorithm Contests (Rujia Liu):: Volume 1. Elementary Problem Solving:: Maths-misc

Very classical mathematical deduction!!!

First, according to test instructions a[i] = (A[i-1] + a[i+1])/2-c[i];

Transform can get a[i+1] = (A[i] + c[i]) * 2-a[i-1];

Then a[n+1] = (A[n] + c[n]) * 2-a[n-1]

= [(A[n-1] + c[n-1]) * 2-a[n-2] + c[n]] * 2-a[n-1]

= 3*a[n-1]-2*a[n-2] + 4*c[n-1] + 2*c[n]

= 4*a[n-2]-3*a[n-3] + 6*c[n-2] + 4*c[n-1] + 2*c[n]

= 5*a[n-3]-4*a[n-4] +8*c[n-3] + 6*C[n-2] + 4*c[ N-1] + 2*C[n]

....

= (n+1) *a-n *a + (n+1-i) * 2 * c[i] + ....

Then A * (n+1) = a[n+1] + n*a-(n+1-i) *2*c[i] + .....

The hand knocks really slow ...

AC Code:

Uva-10014-simple Calculations (Classic math derivation!!) ）

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