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| class Solution {
public int[] findOrder(int numCourses, int[][] prerequisites) {
Map<Integer, List<Integer>> courseDependentMap = new HashMap<>();
Map<Integer, Integer> preCount = new HashMap<>();
Queue<Integer> queue = new LinkedList<>();
int pos = 0;
int[] result = new int[numCourses];
for (int i = 0; i < numCourses; i++) {
preCount.put(i, 0);
}
for (int[] prerequisite : prerequisites) {
courseDependentMap.putIfAbsent(prerequisite[1], new ArrayList<>());
courseDependentMap.get(prerequisite[1]).add(prerequisite[0]);
preCount.put(prerequisite[0], preCount.get(prerequisite[0]) + 1);
}
for (Map.Entry<Integer, Integer> entry : preCount.entrySet()) {
if (entry.getValue() == 0) {
queue.offer(entry.getKey());
}
}
while (!queue.isEmpty()) {
int currCourse = queue.poll();
result[pos] = currCourse;
pos += 1;
if (courseDependentMap.containsKey(currCourse)) {
for (Integer dependent : courseDependentMap.get(currCourse)) {
preCount.put(dependent, preCount.get(dependent) - 1);
if (preCount.get(dependent) == 0) {
queue.offer(dependent);
}
}
courseDependentMap.remove(currCourse);
}
}
return courseDependentMap.isEmpty() ? result : new int[0];
}
}
|
