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class Solution {
public:
bool canFinish(int n, vector<vector<int>>& p) {
vector<vector<int>> g(n);
vector<int> d(n);
for(auto &i: p)
{
int x = i[0], y = i[1];
g[x].push_back(y);
d[y]++;
}
queue<int> q;
int ans = 0;
for(int i = 0; i < n; i++)
if(!d[i]) q.push(i);
while(q.size())
{
auto t = q.front();
q.pop();
ans++;
for(auto &i: g[t])
if(--d[i] == 0) q.push(i);
}
return ans == n;
}
};