1172. Ship Routes

http://acm.timus.ru/problem.aspx?space=1&num=1172

水题DP   大整数直接上java

代码：

import java.math.BigInteger;

import java.util.Scanner;



public class Main {



	/**

	 * @param args

	 */

	static final int N = 35;



	public static void main(String[] args) {

		// TODO Auto-generated method stub

		Scanner in = new Scanner(System.in);

		BigInteger[][][][] dp = new BigInteger[N][N][N][4];

		int n = in.nextInt();

		for (int i = 0; i <= n; ++i) {

			for (int j = 0; j <= n; ++j) {

				for (int l = 0; l <= n; ++l) {

					for (int k = 1; k <= 3; ++k) {

						dp[i][j][l][k]=BigInteger.ZERO;

					}

				}

			}

		}

		dp[0][0][0][1] = BigInteger.ONE;

		for (int i = 0; i <= n; ++i) {

			for (int j = 0; j <= n; ++j) {

				for (int l = 0; l <= n; ++l) {

					for (int k = 1; k <= 3; ++k) {

						if (dp[i][j][l][k].compareTo(BigInteger.ZERO) == 1) {

							if (k != 1 && i < n) {

								dp[i + 1][j][l][1] = dp[i + 1][j][l][1]

										.add(dp[i][j][l][k].multiply(BigInteger

												.valueOf(Math.max(1, n - i - 1))));

							}

							if (k != 2 && j < n) {

								dp[i][j + 1][l][2] = dp[i][j + 1][l][2]

										.add(dp[i][j][l][k].multiply(BigInteger

												.valueOf(n - j)));

							}

							if (k != 3 && l < n) {

								dp[i][j][l + 1][3] = dp[i][j][l + 1][3]

										.add(dp[i][j][l][k].multiply(BigInteger

												.valueOf(n - l)));

							}

						}

					}

				}

			}

		}

		System.out.println(dp[n][n][n][1].divide(BigInteger.valueOf(2L)));

	}



}