uva 1464 - Traffic Real Time Query System（双联通+LCA）

#include <cstdio>
#include <cstring>
#include <vector>
#include <stack>
#include <algorithm>

using namespace std;
typedef pair<int,int> pii;
const int maxn = 10005;
const int maxm = 100005;

int N, M, eccno[maxm];
int cntlock, cntbcc, pre[maxn], iscut[maxn], bccno[maxn];
int E, first[maxn], jump[maxm << 1], link[maxm << 1];
vector<int> G[maxn << 1], BCC[maxn], tmp;
stack<pii> S;

inline void addEdge(int u, int v) {
jump[E] = first[u];
link[E] = v;
first[u] = E++;
}

int dfs (int u, int fa) {
int lowu = pre[u] = ++cntlock, child = 0;

for (int i = first[u]; i != -1; i = jump[i]) {
int v = link[i];
pii e = make_pair(u, v);

if (!pre[v]) {
child++;
S.push(e);
int lowv = dfs(v, u);
lowu = min(lowu, lowv);
if (lowv >= pre[u]) {
iscut[u] = 1;
BCC[++cntbcc].clear();
while (true) {
e = S.top(); S.pop();
if (bccno[e.first] != cntbcc) {
bccno[e.first] = cntbcc;
BCC[cntbcc].push_back(e.first);
}
if (bccno[e.second] != cntbcc) {
bccno[e.second] = cntbcc;
BCC[cntbcc].push_back(e.second);
}
if (e.first == u && e.second == v) break;
}
}
} else if (pre[v] < pre[u] && v != fa) {
S.push(e);
lowu = min(lowu, pre[v]);
}
}

if (fa < 0 && child == 1) iscut[u] = 0;
return lowu;
}

void findBCC() {
cntlock = cntbcc = 0;
memset(pre, 0, sizeof(pre));
memset(iscut, 0, sizeof(iscut));
memset(bccno, 0, sizeof(bccno));
for (int i = 1; i <= N; i++)
if (!pre[i]) dfs(i, -1);
}

void init () {
E = 0;
memset(first, -1, sizeof(first));

int u, v;
for (int i = 0; i < M; i++) {
scanf("%d%d", &u, &v);
addEdge(u, v);
addEdge(v, u);
}
findBCC();

for (int i = 1; i <= cntbcc; i++) {
G[i].clear();
for (int j = 0; j < BCC[i].size(); j++) bccno[BCC[i][j]] = i;
for (int j = 0; j < BCC[i].size(); j++) {
for (int p = first[BCC[i][j]]; p != -1; p = jump[p])
if (bccno[link[p]] == i) eccno[p>>1] = i;
}
}

int c = 0;
for (int i = 1; i <= N; i++) {
if (iscut[i]) {
c++;
G[cntbcc + c].clear();

tmp.clear();
for (int j = first[i]; j != -1; j = jump[j])
tmp.push_back(eccno[j>>1]);
sort(tmp.begin(), tmp.end());
int n = unique(tmp.begin(), tmp.end()) - tmp.begin();
for (int j = 0; j < n; j++) {
G[cntbcc+c].push_back(tmp[j]);
G[tmp[j]].push_back(cntbcc+c);
//printf("%d-%d\n", cntbcc + c, tmp[j]);
}
}
}
N = cntbcc + c;
}

const int maxd = 18;
int vis[maxn << 1], dep[maxn << 1], dp[maxn << 1][maxd];

void dfs (int u, int fa, int d) {
dep[u] = d;
dp[u][0] = fa;
vis[u] = 1;
for (int i = 1; i < maxd; i++)
dp[u][i] = dp[dp[u][i-1]][i-1];
for (int i = 0; i < G[u].size(); i++) {
int v = G[u][i];
if (vis[v]) continue;
dfs(v, u, d + 1);
}
}

void LCAinit() {
memset(vis, 0, sizeof(vis));
for (int i = 1; i <= N; i++)
if (!vis[i]) dfs(i, 0, 0);
}

int LCA(int a, int b) {
if (dep[a] < dep[b]) swap(a, b);
int k = 0;
while ((1<<(k+1)) <= dep[a]) k++;
for (int i = k; i >= 0; i--)
if (dep[a]-(1<<i) >= dep[b]) a = dp[a][i];
if (a == b) return a;

for (int i = k; i >= 0; i--) {
if (dp[a][i] != dp[b][i]) {
a = dp[a][i];
b = dp[b][i];
}
}
return dp[a][0];
}

int main () {
while (scanf("%d%d", &N, &M) == 2 && N + M) {
init();
LCAinit();

int q, u, v, f;
scanf("%d", &q);
while (q--) {
scanf("%d%d", &u, &v);
u = eccno[u-1];
v = eccno[v-1];
f = LCA(u, v);
printf("%d\n", (dep[u] + dep[v] - 2 * dep[f]) >> 1);
}
}
return 0;
}