310. Minimum Height Trees LeetCode

class Solution {
public:
vector<int> findMinHeightTrees(int n, vector<pair<int, int>>& edges) {
if(n == 1) return vector<int>{0};
vector<vector<int>> edge;
vector<int> vis,d,ans;
for(int i = 0; i <= n; i++)
{
edge.push_back(vector<int>{});
vis.push_back(0);
d.push_back(0);
}
for(int i = 0; i < edges.size(); i++)
{
int u = edges[i].first;
int v = edges[i].second;
edge[u].push_back(v);
edge[v].push_back(u);
d[u]++;
d[v]++;
}
queue<int> q;
while(!q.empty()) q.pop();
for(int i = 0; i < n; i++)
if(d[i] == 1) q.push(i),vis[i] = 1;
while(!q.empty())
{
int n = q.size();
ans.clear();
for(int k = 1; k <= n; k++)
{
int now = q.front();
q.pop();
ans.push_back(now);
for(int i = 0; i < edge[now].size(); i++)
{
int v = edge[now][i];
if(!vis[v])
{
d[v]--;
if(d[v] == 1)
{
q.push(v);
vis[v] = 1;
}
}
}
}
}
return ans;
}
};