コード
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
struct HL {
vector<vector<int>> g;
vector<int> vertexID, depth, head, parent, size;
int u, v, k;
HL(const vector<vector<int>> &adj) {
g = adj;
vertexID.resize(adj.size());
depth.resize(adj.size());
head.resize(adj.size());
parent.resize(adj.size());
size.assign(adj.size(), 1);
k = 0;
dfs(0, -1);
dfs2(0, -1);
}
void dfs(int curr, int prev) {
head[curr] = curr;
parent[curr] = prev;
for (int &next : g[curr]) {
if (next == prev) continue;
depth[next] = depth[curr] + 1;
dfs(next, curr);
size[curr] += size[next];
int &h = g[curr][0];
if (h == prev || size[h] < size[next]) swap(h, next);
}
}
void dfs2(int curr, int prev) {
vertexID[curr] = k++;
if (g[curr].size() > 1) head[g[curr][0]] = head[curr];
for (int next : g[curr])
if (next != prev) dfs2(next, curr);
}
void set(int x, int y) {
u = x;
v = y;
}
bool same(int u, int v) { return head[u] == head[v]; }
pair<int, int> next() {
if (depth[u] > depth[v]) swap(u, v);
if (depth[head[u]] > depth[head[v]]) swap(u, v);
int l = same(u, v) ? vertexID[u] : vertexID[head[v]];
int r = vertexID[v] + 1;
v = same(u, v) ? -1 : parent[head[v]];
return {l, r};
}
bool hasNext() { return v != -1; }
};
struct LCA {
LCA() {}
vector<vector<int>> G;
vector<vector<int>> parent;
vector<int> depth;
int root, logV;
void dfs(int v, int p, int d) {
parent[0][v] = p;
depth[v] = d;
for (auto &u : G[v])
if (u != p) dfs(u, v, d + 1);
}
LCA(const vector<vector<int>> &adj) {
int V = adj.size();
root = 0;
G = adj;
depth.assign(V, 0);
logV = 1;
for (int i = 1; i <= V;) i *= 2, logV++;
parent.assign(logV, vector<int>(V));
dfs(root, -1, 0);
for (int k = 0; k + 1 < logV; ++k)
for (int v = 0; v < V; ++v)
if (parent[k][v] < 0) {
parent[k + 1][v] = -1;
} else {
parent[k + 1][v] = parent[k][parent[k][v]];
}
}
int getLCA(int u, int v) {
if (depth[u] > depth[v]) swap(u, v);
for (int k = 0; k < logV; ++k)
if ((depth[v] - depth[u]) >> k & 1) v = parent[k][v];
if (u == v) return u;
for (int k = logV - 1; k >= 0; --k)
if (parent[k][u] != parent[k][v]) {
u = parent[k][u];
v = parent[k][v];
}
return parent[0][u];
}
int getLength(int u, int v) {
int lca = getLCA(u, v);
return depth[u] + depth[v] - depth[lca] * 2;
}
};
struct RMQ {
static const int N = 1 << 17;
vector<long long> seg;
RMQ() : seg(N * 2, (long long)1e18) {}
void update(int k, long long value) {
seg[k += N - 1] = value;
while (k > 0) {
k = (k - 1) / 2;
seg[k] = min(seg[k * 2 + 1], seg[k * 2 + 2]);
}
}
long long query(int a, int b, int k = 0, int l = 0, int r = N) {
if (r <= a || b <= l) return 1e18;
if (a <= l && r <= b) return seg[k];
long long x = query(a, b, k * 2 + 1, l, (l + r) / 2);
long long y = query(a, b, k * 2 + 2, (l + r) / 2, r);
return min(x, y);
}
};
int main() {
cin.tie(0);
ios::sync_with_stdio(false);
int N, Q;
cin >> N >> Q;
vector<vector<int>> adj(N, vector<int>());
for (int i = 0; i < N - 1; ++i) {
int A, B;
cin >> A >> B;
A--, B--;
adj[A].push_back(B);
adj[B].push_back(A);
}
LCA lca(adj);
HL hl(adj);
RMQ rmq1, rmq2;
string S;
cin >> S;
queue<pair<int, int>> que;
for (int i = 0; i < N; ++i)
if (S[i] == '1') que.push({i, 0});
vector<int> cost(N, N);
while (!que.empty()) {
pair<int, int> p = que.front();
que.pop();
if (cost[p.first] <= p.second) continue;
cost[p.first] = p.second;
for (const auto &v : adj[p.first]) que.push({v, p.second + 1});
}
for (int i = 0; i < N; ++i) {
rmq1.update(hl.vertexID[i], cost[i] * 3 - hl.depth[i]);
rmq2.update(hl.vertexID[i], cost[i] * 3 + hl.depth[i]);
}
while (Q--) {
int s, t;
cin >> s >> t;
s--, t--;
int d = lca.getLength(s, t);
int l = lca.getLCA(s, t);
ll ans = d * 2;
ll min1 = 1e9;
hl.set(s, l);
while (hl.hasNext()) {
pair<int, int> p = hl.next();
min1 = min(min1, rmq1.query(p.first, p.second));
}
ans = min(ans, d + hl.depth[s] + min1);
ll min2 = 1e9;
hl.set(t, l);
while (hl.hasNext()) {
pair<int, int> p = hl.next();
min2 = min(min2, rmq2.query(p.first, p.second));
}
ans = min(ans, d + hl.depth[s] - hl.depth[l] * 2 + min2);
cout << ans << endl;
}
}