poj 1207(拓扑排序用到了深搜)

拓扑排序的思想：
1：从有向图中选一个无前驱的顶点输出；
2：将此顶点和以它为起点的弧删除；
3：重复1和2，直到不存在无前驱的顶点；
4：若此时输出的顶点数小于有向图中的顶点数，则说明有向图中存在回路，否则输出的顶点的顺序即为一个拓扑序列。

package com.liang.poj;

import java.util.Arrays;
import java.util.Scanner;

public class Test1270Tuo_Pu {
	static StringBuffer strb1 = new StringBuffer();
	static int[] count = null;
	static int[][] relation = null;
	static String str1 = "";
	static String str2 = "";
	static char[] result = null;
	static boolean[] visited = null;
	static int[] tag = null;
	static int[][] liang = null;
	static int sum = 0;

	public static void main(String[] args) throws Exception{
		Scanner scan = new Scanner(System.in);

		str1 = scan.nextLine();
		str2 = scan.nextLine();

		for (int i = 0; i < str1.length(); i += 2) {
			strb1.append(str1.charAt(i));
		}

		sum = strb1.length();
		relation = new int[sum][sum];
		count = new int[sum];
		result = new char[sum];
		visited = new boolean[sum];
		Arrays.fill(visited, false);
		tag = new int[sum];
		liang = new int[sum][sum];

		makeSet();
		dfs(0);
	}

	public static void makeSet() {
		for (int i = 0; i < str2.length(); i += 4) {
			int a = 0;
			int b = 0;
			for (int j = 0; j < strb1.length(); j++) {
				if (str2.charAt(i) == strb1.charAt(j)) {
					a = j;
					break;
				}
			}

			for (int j = 0; j < strb1.length(); j++) {
				if (str2.charAt(i + 2) == strb1.charAt(j)) {
					b = j;
					count[j]++;
					break;
				}
			}

			relation[a][b] = 1;
		}
	}

	public static void dfs(int geshu) {
		if (geshu >= sum) {
			show();
			return;
		}
		for (int i = 0; i < count.length; i++) {
			if (count[i] == 0 && !visited[i]) {
				result[geshu] = strb1.charAt(i);
				visited[i] = true;
				for (int j = 0; j < relation.length; j++) {
					if (relation[i][j] != 0) {
						count[j]--;
						tag[j]++;
						liang[i][j] = 1;
					}
				}
				dfs(geshu + 1);
				visited[i] = false;
				for (int j = 0; j < relation.length; j++) {
					if (tag[j] != 0 && liang[i][j] != 0) {
						count[j]++;
						tag[j]--;
						liang[i][j] = 0;
					}
				}
			}
		}
	}

	public static void show() {
		for (int i = 0; i < result.length; i++) {
			System.out.print(result[i]);
		}
		System.out.println();
	}

}