洛谷1002优化算法_加法定理

// 洛谷1002优化算法_加法定理.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>
using namespace std;


int main()
{
	int bx, by, cx, cy;
	long long f[25][25];	
	cin >> bx >> by >> cx >> cy;
	for (int i = 0; i <= bx; i++)
	{
		for (int j = 0; j <= by; j++)
		{
			if ((i == (cx - 2) && j == (cy - 1))
				|| (i == (cx - 2) && j == (cy + 1))
				|| (i == (cx - 1) && j == (cy - 2))
				|| (i == (cx - 1) && j == (cy + 2))
				|| (i == (cx + 1) && j == (cy - 2))
				|| (i == (cx + 1) && j == (cy + 2))
				|| (i == (cx + 2) && j == (cy - 1))
				|| (i == (cx + 2) && j == (cy + 1))
				|| (i == cx && j == cy)
				)
				f[i][j] = -1;
			else
				f[i][j] = 0;
		}
	}
	f[0][0] = 1;
	for (int i = 0; i <= bx; i++)
	{
		for (int j = 0; j <= by; j++)
		{
			if (f[i][j] != -1)
			{
				if (i&&f[i - 1][j] != -1) 
					f[i][j] += f[i - 1][j];
				if (j&&f[i][j - 1] != -1) 
					f[i][j] += f[i][j - 1];
			}
		}
	}
	cout << f[bx][by];
	return 0;
}