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8/6/2018 - 3:48 AM

796

UVA 796, c++, articulation points and bridges problem (bridges only)

``````// Problem #    : 796
// Created on   : 2018-08-05 21:18:56

#include <bits/stdc++.h>

#define FOR(i, n) for (int i = 0; i < (int)n; ++i)
#define FOREACH(i, c)                                                          \
for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ALL(c) (c).begin(), (c).end()
#define UNIQUE(c) (c).resize(unique(ALL(c)) - (c).begin())
#define MP make_pair
#define L first
#define R second

using namespace std;

typedef long long ll;
typedef pair<int, int> ii; // pair of ints
typedef vector<int> vi;    // 1d vector of ints
typedef vector<ii> vii;    // 1d vector of pairs

int d, r, c;
vi num, lo, p;
vector<vi> g;
vii B; // bridges

// Just for bridges, removed stuff specific to finding points
void apb(int u) {
lo[u] = num[u] = d++;
for (auto &v : g[u]) {
if (num[v] == -1) {
p[v] = u;
apb(v);

if (lo[v] > num[u])
B.push_back(ii(min(u, v), max(u, v)));

lo[u] = min(lo[u], lo[v]);
} else if (v != p[u]) {
lo[u] = min(lo[u], num[v]);
}
}
}

// Articulation points and bridges problem, want to find # of bridges and print
// what the are.
int main() {

int V;
while (scanf(" %d", &V) == 1) {
if (V == 0) {
continue;
}

g.assign(V, vi());

int u, v, e;
for (int i = 0; i < V; i++) {
scanf("%d (%d)", &u, &e);
FOR(i, e) {
scanf(" %d", &v);
g[u].push_back(v);
}
}

// init
d = 0;
num.assign(V, -1);
lo.assign(V, 0);
p.assign(V, -1);
B.clear();

// NOTE: we are skipping some steps here related to gathering the
// articulation points because we only care about bridges for this problem.
FOR(i, V) {
if (num[i] == -1) {
apb(i);
}
}