Uva 10305 Ordering Tasks（拓扑排序）

/*
Kahn 算法 复杂度：O(E+V)
L← Empty list that will contain the sorted elements
S ← Set of all nodes with no incoming edges
while S is non-empty do
remove a node n from S
insert n into L
for each node m with an edge e from n to m do
remove edge e from the graph
if m has no other incoming edges then
insert m into S
if graph has edges then
return error (graph has at least onecycle)
else
return L (a topologically sortedorder)
*/

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
int n,m;
int graph[105][105];
int indegree[105];
int ret[105];
queue <int> q;
void toposort(){
for(int i=1;i<=n;i++){
if(!indegree[i])
q.push(i);
}
int cnt=0;
while(!q.empty()){
int tmp=q.front();q.pop();
ret[++cnt]=tmp;
for(int i=1;i<=n;i++){
if(graph[tmp][i]==1){
graph[tmp][i]--;
q.push(i);
}
}
}
for(int i=1;i<=n;i++){
if(i!=n){
printf("%d ",ret[i]);
}
else{
printf("%d\n",ret[i]);
}
}
}
int main(){
while(scanf("%d %d",&n,&m)!=EOF&&(m||n)){
memset(graph,0,sizeof(graph));
memset(indegree,0,sizeof(indegree));
memset(ret,0,sizeof(ret));
for(int i=1;i<=m;i++){
int a,b;
scanf("%d %d",&a,&b);
if(!graph[a][b]){
graph[a][b]=1;
indegree[b]++;
}
}
toposort();
}
return 0;
}

/*
基于DFS的拓扑排序
L ← Empty list that will contain the sorted nodes
S ← Set of all nodes with no outgoing edges
for each node n in S do
visit(n)
function visit(node n)
if n has not been visited yet then
mark n as visited
for each node m with an edgefrom m to ndo
visit(m)
add n to L
*/

#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
const int maxn = 101;
int n, m, t;
int gragh[maxn][maxn], res[maxn], c[maxn];

bool dfs(int u) {
c[u] = -1;
for (int v = 0; v < n; v++)
if (gragh[u][v])
if (c[v] < 0)
return false;
else if (!c[v] && !dfs(v))
return false;
c[u] = 1;
res[--t] = u;
return true;
}

bool toposort() {
t = n;
memset(c, 0, sizeof(c));
for (int u = 0; u < n; u++)
if (!c[u])
if (!dfs(u))
return false;
return true;
}

int main() {
while (scanf("%d%d", &n, &m) && (n || m)) {
memset(gragh, 0, sizeof(gragh));
int a, b;
for (int i = 0; i < m; i++) {
scanf("%d%d", &a, &b);
gragh[a-1][b-1] = 1;
}
toposort();
for (int i = 0; i < n; i++)
printf("%d ", res[i] + 1);
printf("\n");
}
return 0;
}