https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_PRoblem&problem=1246

題目：

John has n tasks to do. Unfortunately, the tasks are not independent and the execution of one task is only possible if other tasks have already been executed.

Input

The input will consist of several instances of the problem. Each instance begins with a line containing two integers,1 <= n <= 100andm.nis the number of tasks (numbered from1ton) andmis the number of direct precedence relations between tasks. After this, there will bemlines with two integersiandj, representing the fact that taskimust be executed before taskj. An instance withn = m = 0will finish the input.

Output

For each instance, print a line withnintegers representing the tasks in a possible order of execution.

Sample Input

5 4
1 2
2 3
1 3
1 5
0 0
Sample Output
1 4 2 5 3題目大意：約翰有n個(gè)任務(wù)要做， 不幸的是，這些任務(wù)并不是獨(dú)立的，執(zhí)行某個(gè)任務(wù)之前要先執(zhí)行完其他相關(guān)聯(lián)的任務(wù)。/
import java.util.Arrays;import java.util.Scanner;public class Main {	static int[][] G;//圖	static int[] c;//判斷每個(gè)節(jié)點(diǎn)的訪(fǎng)問(wèn)狀態(tài)	static int[] topo;//記錄拓?fù)渑判虻慕Y(jié)果	static int m,n,t;	public static void main(String[] args) {		Scanner scan = new Scanner(System.in);		while(true){			n = scan.nextInt();			m = scan.nextInt();			if((m+n)==0)				break;						G = new int[n+1][n+1];			c = new int[n+1];			topo = new int[n+1];			for(int i=1;i<=n;i++){				for(int j=1;j<=n;j++){					G[i][j] = 0;				}			}			Arrays.fill(c, 0);			for(int i=0;i<m;i++){				int a = scan.nextInt();				int b = scan.nextInt();				G[a][b] = 1;			}						if(topsort()){				String str = "";				for(int i=1;i<=n;i++){					str+=topo[i]+" ";				}				System.out.println(str.trim());			}else{				System.out.println("No");			}								}	}	//dfs	public static boolean dfs(int u){		c[u] = -1;		for(int v = 1;v<=n;v++) if(G[u][v]==1){			if(c[v]==-1)				return false;			else if(c[v]==0&&!dfs(v))				return false;		}		c[u] = 1;		topo[--t] = u;//		System.out.println(u);		return true;	}	public static boolean topsort(){		t = n+1;		for(int u=1;u<=n;u++){			if(c[u]==0&&!dfs(u)){				return false;			}		}		return true;	}}