Create 1462.Course-Schedule-IV.cpp

Author: wisdompeak

BFS/1462.Course-Schedule-IV/1462.Course-Schedule-IV.cpp

@@ -0,0 +1,46 @@
+class Solution {
+public:
+ vector<bool> checkIfPrerequisite(int n, vector<vector<int>>& prerequisites, vector<vector<int>>& queries) 
+ {
+ vector<unordered_set<int>>next(n);
+ vector<int>inDegree(n,0);
+ vector<unordered_set<int>>preSet(n);
+ 
+ for (auto edge: prerequisites)
+ {
+ next[edge[0]].insert(edge[1]);
+ inDegree[edge[1]] += 1;
+ }
+ 
+ queue<int>q;
+ for (int i=0; i<n; i++)
+ {
+ preSet[i].insert(i);
+ if (inDegree[i]==0)
+ q.push(i);
+ } 
+ 
+ while (!q.empty())
+ {
+ int cur = q.front();
+ q.pop();
+ 
+ for (int next: next[cur])
+ {
+ for (auto x: preSet[cur])
+ preSet[next].insert(x);
+ 
+ inDegree[next] -= 1;
+ if (inDegree[next]==0)
+ q.push(next);
+ }
+ }
+ 
+ vector<bool>rets;
+ for (auto query: queries)
+ {
+ rets.push_back(preSet[query[1]].find(query[0])!=preSet[query[1]].end());
+ }
+ return rets;
+ }
+};