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#include "leetcode.h"
class Solution {
public:
vector<vector<int>> criticalConnections(int n,
vector<vector<int>> &connections) {
vector<bool> vi(n, false);
vector<int> disc(n, 0), low(n, 0), parent(n, -1);
vector<vector<int>> g(n, vector<int>()), ans;
for (auto &p : connections) {
g[p.front()].push_back(p.back());
g[p.back()].push_back(p.front());
}
for (int i = 0; i < n; ++i) {
if (vi[i])
continue;
helper(i, vi, disc, low, parent, g, ans);
}
return ans;
}
private:
void helper(int u, vector<bool> &vi, vector<int> &disc, vector<int> &low,
vector<int> &parent, vector<vector<int>> &g,
vector<vector<int>> &ans) {
static int time = 0;
vi[u] = true;
disc[u] = low[u] = ++time;
for (int i : g[u]) {
if (!vi[i]) {
parent[i] = u;
helper(i, vi, disc, low, parent, g, ans);
low[u] = min(low[u], low[i]);
if (low[i] > disc[u])
ans.push_back({u, i});
} else if (i != parent[u])
low[u] = min(low[u], disc[i]);
}
}
};
int main() {}
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