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210.java
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210.java
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__________________________________________________________________________________________________
sample 2 ms submission
class Solution {
public int[] findOrder(int numCourses, int[][] prerequisites) {
List[] course=new List[numCourses];
int[] map=new int[numCourses];
List<Integer> ans = new ArrayList<Integer>();
for(int i=0;i<numCourses;i++){
course[i]=new ArrayList<Integer>();
}
for(int i=0;i<prerequisites.length;i++){
course[prerequisites[i][0]].add(prerequisites[i][1]);
}
for(int i=0;i<numCourses;i++){
if(dfs(course,i,ans,map)==false) {
return new int[0];
}
}
int[] an = new int[ans.size()];
for(int i = 0; i < ans.size(); i++){
an[i] = ans.get(i);
}
return an;
}
public boolean dfs(List[] course,int req,List<Integer> ans,int[] map) {
//post-order traverse
if(map[req] == 0) {
map[req] = 1;
for(int i=0;i<course[req].size();i++) {
if(dfs(course,(int)course[req].get(i),ans,map)==false) {
return false;
}
}
map[req]=2;
} else if(map[req]==1) {
return false;
} else if(map[req]==2) {
return true;
}
ans.add(req);
return true;
}
}
__________________________________________________________________________________________________
sample 36820 kb submission
class Solution {
public int[] findOrder(int numCourses, int[][] prerequisites) {
int[] indegree = new int[numCourses];
for(int[] pre:prerequisites){
indegree[pre[0]]++;
}
int count=0;
int[] res = new int[numCourses];
Queue<Integer> q = new LinkedList<>();
for(int i=0;i<numCourses;i++){
if(indegree[i]==0){
q.offer(i);
}
}
while(!q.isEmpty()){
int cur = q.poll();
res[count++]=cur;
for(int[] pre:prerequisites){
if(pre[1]==cur){
--indegree[pre[0]];
if(indegree[pre[0]]==0){
q.offer(pre[0]);}
}
}
}
return count==numCourses?res:new int[0];
}
}
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