天平 (Not so Mobile, UVa 839)

#include <iostream>
using namespace std;

#define IsLeaf(w1, w2) ((w1) && (w2))
bool solve(int &w)
{
	int W1, L1, W2, L2;
	cin>> W1 >> L1 >> W2 >> L2;
	if(IsLeaf(W1, W2) == true)
	{
		//Leaf节点表示递归终止
		w = W1 + W2;
		return (W1 * L1 == W2 * L2);
	}
	else
	{
		bool b1 = true, b2 = true;
		if(!W1) b1 = solve(W1);	//Node节点进行递归
		if(!W2) b2 = solve(W2);	//Node节点进行递归
		w = W1 + W2;
		return b1 && b2 && (W1 * L1 == W2 * L2);
	}
}

int main()
{
	int w = 0;
	if(solve(w)) cout<< "YES";
	else cout<< "NO";
	return 0;
}