Uva 839 Not so Mobile

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Not so Mobile

Before being an ubiquous communications gadget, a mobile was just a structure made of strings and wires suspending colourfull things. This kind of mobile is usually found hanging over cradles of small babies.

 

The figure illustrates a simple mobile. It is just a wire, suspended by a string, with an object on each side. It can also be seen as a kind of lever with the fulcrum on the point where the string ties the wire. From the lever principle we know that to balance a simple mobile the product of the weight of the objects by their distance to the fulcrum must be equal. That is Wl×Dl = Wr×Dr where Dl is the left distance, Dr is the right distance, Wl is the left weight and Wr is the right weight.

 

In a more complex mobile the object may be replaced by asub-mobile, as shown in the next figure. In this case it is not sostraightforward to check if the mobile is balanced so we need youto write a program that, given a description of a mobile as input,checks whether the mobile is in equilibrium or not.

 

 

Input 

The input begins with a single positive integer on a line by itself indicatingthe number of the cases following, each of them as described below.This line is followed by a blank line, and there is also a blank line betweentwo consecutive inputs.

 

The input is composed of several lines, each containing 4 integersseparated by a single space. The 4 integers represent thedistances of each object to the fulcrum and their weights, in theformat: Wl Dl Wr Dr

If Wl or Wr is zero then there is a sub-mobile hanging fromthat end and the following lines define the the sub-mobile. Inthis case we compute the weight of the sub-mobile as the sum ofweights of all its objects, disregarding the weight of the wiresand strings. If both Wl and Wr are zero then the followinglines define two sub-mobiles: first the left then the right one.

 

Output 

For each test case, the output must follow the description below.The outputs of two consecutive cases will be separated by a blank line.

 

Write `YES‘ if the mobile is in equilibrium, write `NO‘ otherwise.

 

Sample Input 

10 2 0 40 3 0 11 1 1 12 4 4 21 6 3 2

 

Sample Output 

YES
本題極為重要！！！

 1 #include<iostream>   2 #include<string.h>   3 #include<stdio.h>   4 #include<ctype.h>   5 #include<algorithm>   6 #include<stack>   7 #include<queue>   8 #include<set>   9 #include<math.h>  10 #include<vector>  11 #include<map>  12 #include<deque>  13 #include<list>  14 using namespace std;  15 bool solve(int& W)16 {17     int W1,D1,W2,D2;18     bool b1=true,b2=true;19     cin>>W1>>D1>>W2>>D2;20     if(!W1)b1=solve(W1);21     if(!W2)b2=solve(W2);22     W=W1+W2;23     return b1 && b2 && (W1*D1==W2*D2); 24 } 25 int main()26 {27     int T,W;28     cin>>T;29     while(T--)30     {31         if(solve(W))32         cout<<"YES\n";33         else34         cout<<"NO\n";35         if(T)36         printf("\N");37     }38     return 0;39 } 

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