Here is the bridge detection algorithm:
timer = 0
disc = array of size n, all -1
low = array of size n
bridges = empty list
function dfs(v, parent):
disc[v] = low[v] = timer
timer = timer + 1
for w in adj[v]:
if w == parent:
continue
if disc[w] == -1:
dfs(w, v)
low[v] = min(low[v], low[w])
if low[w] > disc[v]:
bridges.append((v, w))
else:
low[v] = min(low[v], disc[w])
for v from 0 to n - 1:
if disc[v] == -1:
dfs(v, -1)
An edge is a bridge if low[w] > disc[v].