2013
11-11

# Incomplete chess boards

Background

Tom gets a riddle from his teacher showing 42 chess boards from each of which two squares are removed. The teacher wants to know which boards can be completely covered by 31 dominoes. He promises ten bars of chocolate for the person who solves the problem correctly. Tom likes chocolate, but he cannot solve this problem on his own. So he asks his older brother John for help. John (who likes chocolate as well) agrees, provided that he will get half the prize.

John’s abilities lie more in programming than in thinking and so decides to write a program. Can you help John? Unfortunately you will not win any bars of chocolate, but it might help you win this programming contest.

Problem

You are given are 31 dominoes and a chess board of size 8 * 8, two distinct squares of which are removed from the board. The square in row a and column b is denoted by (a, b) with a, b in {1, . . . , 8}.

A domino of size 2 × 1 can be placed horizontally or vertically onto the chess board, so it can cover either the two squares {(a, b), (a, b + 1)} or {(b, a), (b + 1, a)} with a in {1, . . . , 8} and b in {1, . . . , 7}. The object is to determine if the so-modified chess board can be completely covered by 31 dominoes.

For example, it is possible to cover the board with 31 dominoes if the squares (8, 4) and (2, 5) are removed, as you can see in Figure 1.

The first input line contains the number of scenarios k. Each of the following k lines contains four integers a, b, c, and d, separated by single blanks. These integers in the range {1, . . . , 8} represent the chess board from which the squares (a, b) and (c, d) are removed. You may assume that (a, b) != (c, d).

The output for every scenario begins with a line containing “Scenario #i:”, where i is the number of the scenario starting at 1. Then print the number 1 if the board in this scenario can be completely covered by 31 dominoes, otherwise write a 0. Terminate the output of each scenario with a blank line.

3
8 4 2 5
8 8 1 1
4 4 7 1

Scenario #1:
1

Scenario #2:
0

Scenario #3:
0

//* @author: ccQ.SuperSupper
import java.io.*;
import java.util.*;

public class Main {

/**
* @param args
*/
public static void main(String[] args)throws Exception {
// TODO Auto-generated method stub
int a,b,c,d,t,i;

Scanner cin = new Scanner(System.in);

t = cin.nextInt();
for(i=1;i<=t;++i){
a = cin.nextInt();
b = cin.nextInt();
c = cin.nextInt();
d = cin.nextInt();

System.out.print("Scenario #"+i);
System.out.println(":");
if((a+b+c+d)%2==1)
System.out.println("1");
else
System.out.println("0");
System.out.println("");
}
}

}

1. 第一题是不是可以这样想，生了n孩子的家庭等价于n个家庭各生了一个1个孩子，这样最后男女的比例还是1:1

2. 这道题这里的解法最坏情况似乎应该是指数的。回溯的时候
O(n) = O(n-1) + O(n-2) + ….
O(n-1) = O(n-2) + O(n-3)+ …
O(n) – O(n-1) = O(n-1)
O(n) = 2O(n-1)

3. 题本身没错，但是HDOJ放题目的时候，前面有个题目解释了什么是XXX定律。
这里直接放了这个题目，肯定没几个人明白是干啥