第八届蓝桥杯省赛-软件类-Java类真题 第二题 标题：纸牌三角形

package com.gxwz.test;

public class Main  {
	
	static int A[] = {1,2,3,4,5,6,7,8,9};		
	static int N = 9*8*7*6*5*4*3*2*1;			//9位数的全排列一共有 9的阶层 次
	static int B[][] = new int [N][A.length];	//二维数组存储全排列
	static int count = 0;	//全排列次数
	static int sum = 0;	//结果
	public static void main(String[] args) {
		f(0,A.length);
		dfs();
//		outB();
//		System.out.println(count);
		System.out.println(sum/6);
	}
	//交换函数
	public static void swap(int i,int j) {
		int temp = A[i];
		A[i] = A[j];
		A[j] = temp;
	}
	//输出数组A
	public static void outA() {
		for (int i : A) {
			System.out.print(i+" ");
		}System.out.println();
	}
	//输出数组B
	public static void outB() {
		for (int[] is : B) {
			for (int i : is) {
				System.out.print(i+" ");
			}System.out.println();
		}
	}
	//把数组A复制给数组B
	public static void copy() {
		for(int i=0;i<A.length;i++) {
			B[count][i] = A[i];
		}
	}
	//递归，全排列
	public static void f(int start,int end) {
		if(start == end - 1) {
//			outA();
			copy();
//			outB();
			count++;
		}else {
			for(int i=start;i<end;i++) {
				swap(i,start);
				f(start+1,end);
				swap(i,start);
			}
		}
	}
	//校验
	public static void dfs() {
		
		for(int i=0;i<B.length;i++) {
			if(B[i][0]+B[i][1]+B[i][2]+B[i][3] == B[i][3]+B[i][4]+B[i][5]+B[i][6] &&
			B[i][3]+B[i][4]+B[i][5]+B[i][6] == B[i][0]+B[i][6]+B[i][7]+B[i][8]) {
				sum++;
			}
		}
	}
}