POJ3687Labeling Balls题解

题目

链接

http://poj.org/problem?id=3687

字面描述

Labeling Balls
Time Limit: 1000MS Memory Limit: 65536K
Total Submissions: 19619 Accepted: 5624
Description

Windy has N balls of distinct weights from 1 unit to N units. Now he tries to label them with 1 to N in such a way that:

No two balls share the same label.
The labeling satisfies several constrains like “The ball labeled with a is lighter than the one labeled with b”.
Can you help windy to find a solution?

Input

The first line of input is the number of test case. The first line of each test case contains two integers, N (1 ≤ N ≤ 200) and M (0 ≤ M ≤ 40,000). The next M line each contain two integers a and b indicating the ball labeled with a must be lighter than the one labeled with b. (1 ≤ a, b ≤ N) There is a blank line before each test case.

Output

For each test case output on a single line the balls’ weights from label 1 to label N. If several solutions exist, you should output the one with the smallest weight for label 1, then with the smallest weight for label 2, then with the smallest weight for label 3 and so on… If no solution exists, output -1 instead.

Sample Input

5

4 0

4 1
1 1

4 2
1 2
2 1

4 1
2 1

4 1
3 2
Sample Output

1 2 3 4
-1
-1
2 1 3 4
1 3 2 4
Source

POJ Founder Monthly Contest – 2008.08.31, windy7926778

思路

可以先筛选编号大的球进行拓扑排序，注意图要反建

代码实现

#include<cstdio>
#include<string.h>
#include<cstring>
#include<stack>
using namespace std;

const int maxn=200+10;
int t,n,m;
int indegree[maxn],topo[maxn];
bool map[maxn][maxn];
inline bool Topo_sort(){
     
	for(int i=n;i>=1;i--){
    
		int temp=-1;
		for(int j=n;j>=1;j--){
    
			if(!indegree[j]){
    
				temp=j;
				break;
			}
		} 
		if(temp==-1)return false;
		indegree[temp]=-1;
		topo[temp]=i;
		for(int j=1;j<=n;j++){
    
			if(map[temp][j])indegree[j]--;
		}
	} 
	return true;
}
int main(){
    
	scanf("%d",&t);
	while(t--){
    
		memset(indegree,0,sizeof(indegree));
		memset(topo,0,sizeof(topo));
		memset(map,false,sizeof(map));
		scanf("%d%d",&n,&m);
		for(int i=1;i<=m;i++){
    
			int x,y;
			scanf("%d%d",&x,&y);
			if(!map[y][x]){
    
				map[y][x]=true;
				indegree[x]++;
			}
		}
		if(!Topo_sort())printf("-1\n");
		else {
    
			for(int i=1;i<=n;i++)printf("%d ",topo[i]);
			printf("\n");
		}
	}
	return 0;
}