This commit is contained in:
Zengtudor 2025-05-03 10:35:33 +08:00
parent b552887e66
commit b1b0c75695
5 changed files with 381 additions and 0 deletions

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src/3/T179940_chat.cpp Normal file
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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
// 定义一个极大值
const ll INF = 1e18;
// 线段树支持区间最小查询和点更新
struct SegmentTree {
int n;
vector<ll> tree;
SegmentTree(int size) {
n = 1;
while(n < size) n <<= 1;
tree.assign(2*n, INF);
}
// 更新位置 pos (0-based) 的值为val
void update(int pos, ll val) {
pos += n;
tree[pos] = min(tree[pos], val);
while(pos > 1){
pos >>= 1;
tree[pos] = min(tree[2*pos], tree[2*pos+1]);
}
}
// 查询区间 [l, r) 的最小值
ll query(int l, int r) const {
ll res = INF;
int left = l + n;
int right = r + n;
while(left < right){
if(left & 1){
res = min(res, tree[left++]);
}
if(right & 1){
res = min(res, tree[--right]);
}
left >>= 1;
right >>= 1;
}
return res;
}
};
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
int n;
ll m;
cin >> n >> m;
vector<ll> a(n);
for(auto &x:a) cin >> x;
// 计算前缀和
vector<ll> s(n+1, 0);
for(int i=1;i<=n;i++) s[i] = s[i-1] + a[i-1];
// 离散化前缀和
vector<ll> all_s = s;
// 还需要 x = s[i] - m
for(int i=0;i<=n;i++) all_s.push_back(s[i] - m);
sort(all_s.begin(), all_s.end());
all_s.erase(unique(all_s.begin(), all_s.end()), all_s.end());
// 映射 s[j] 和 x 到离散化后的索引
auto get_idx = [&](ll val) -> int {
return lower_bound(all_s.begin(), all_s.end(), val) - all_s.begin();
};
int size = all_s.size();
// 初始化两个线段树
SegmentTree st1(size); // 存 dp[j] - s[j]
SegmentTree st2(size); // 存 dp[j] + s[j]
// 初始化 dp[0] = 0
// 插入 j=0 的情况
st1.update(get_idx(s[0]), 0 - s[0]);
st2.update(get_idx(s[0]), 0 + s[0]);
// 初始化 dp array
// 可以不存储全 dp array因为只需要 dp[j] 继续更新下去
vector<ll> dp(n+1, INF);
dp[0] = 0;
for(int i=1;i<=n;i++){
ll x = s[i] - m;
// 找到 x 在 all_s 中的离散化索引
// 对于 st1查询 s[j] <= x
// 找最大的 s[j] <= x即 upper_bound(x) - 1
int pos1 = upper_bound(all_s.begin(), all_s.end(), x) - all_s.begin() - 1;
ll res1 = INF;
if(pos1 >= 0){
res1 = st1.query(0, pos1+1) + x;
}
// 对于 st2查询 s[j] >= x
// 找最小的 s[j] >= x即 lower_bound(x)
int pos2 = lower_bound(all_s.begin(), all_s.end(), x) - all_s.begin();
ll res2 = INF;
if(pos2 < size){
res2 = st2.query(pos2, size) - x;
}
// 取两者最小值作为 dp[i]
dp[i] = min(res1, res2);
// 更新线段树
st1.update(get_idx(s[i]), dp[i] - s[i]);
st2.update(get_idx(s[i]), dp[i] + s[i]);
}
cout << dp[n] << "\n";
}

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#include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
ll n, m;
pair<ll, ll> bfs(ll start, const vector<vector<ll>> &adj) {
vector<ll> dist(n + 1, -1);
queue<ll> q;
q.push(start);
dist[start] = 0;
ll far = start;
while (!q.empty()) {
ll u = q.front(); q.pop();
for (auto &v : adj[u]) {
if (dist[v] == -1) {
dist[v] = dist[u] + 1;
q.push(v);
if (dist[v] > dist[far]) {
far = v;
}
}
}
}
return {far, dist[far]};
}
int main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n >> m;
vector<vector<ll>> adj(n + 1, vector<ll>());
for (ll i = 0; i < m; i++) {
ll u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
vector<bool> vis(n +1, false);
ll sum_d = 0;
ll k = 0;
for(ll u =1; u <=n; u++) {
if(!vis[u]){
k++;
auto [ff, fd1] = bfs(u, adj);
auto [sf, sd] = bfs(ff, adj);
sum_d += sd;
queue<ll> qvis;
qvis.push(u);
vis[u] = true;
while(!qvis.empty()){
ll node = qvis.front(); qvis.pop();
for(auto &v : adj[node]){
if(!vis[v]){
vis[v] = true;
qvis.push(v);
}
}
}
}
}
if(k == 1){
cout << sum_d + 1 << '\n';
}
else{
cout << sum_d + k << '\n';
}
}

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src/3/T225686_chat.cpp Normal file
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#include <bits/stdc++.h>
using namespace std;
using ll = int64_t;
ll n, m;
vector<vector<ll>> adj;
vector<char> vis_marker;
pair<ll, ll> bfs(ll start){
deque<ll> q;
q.push_back(start);
ll farthest_node = start;
ll max_distance = 0;
vector<ll> dist(n + 1, -1);
dist[start] = 0;
vis_marker[start] = 1;
while(!q.empty()){
ll u = q.front();
q.pop_front();
for(auto &v : adj[u]){
if(!vis_marker[v]){
vis_marker[v] = 1;
dist[v] = dist[u] + 1;
q.push_back(v);
if(dist[v] > max_distance){
max_distance = dist[v];
farthest_node = v;
}
}
}
}
return {farthest_node, max_distance};
}
int main(){
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> m;
adj.assign(n + 1, vector<ll>());
ll u, v;
for(ll i = 0; i < m; ++i){
cin >> u >> v;
adj[u].emplace_back(v);
adj[v].emplace_back(u);
}
vis_marker.assign(n + 1, 0);
ll sum_d = 0;
ll k = 0;
for(ll u = 1; u <= n; ++u){
if(!vis_marker[u]){
k++;
pair<ll, ll> first_bfs = bfs(u);
ll ff = first_bfs.first;
pair<ll, ll> second_bfs = bfs(ff);
ll sd = second_bfs.second;
sum_d += sd;
}
}
if(k == 1){
cout << sum_d + 1 << '\n';
}
else{
cout << sum_d + k << '\n';
}
}

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src/3/T585518_chat.cpp Normal file
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#include <bits/stdc++.h>
using namespace std;
// 定义无向图的邻接表表示
vector<vector<int>> adj;
// BFS函数返回从起点开始的所有节点的距离
vector<int> bfs(int start, int n) {
vector<int> dist(n + 1, -1); // 节点编号从1到n
queue<int> q;
q.push(start);
dist[start] = 0;
while (!q.empty()) {
int u = q.front(); q.pop();
for(auto &v : adj[u]) {
if(dist[v] == -1){
dist[v] = dist[u] + 1;
q.push(v);
}
}
}
return dist;
}
int main(){
ios::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
adj.assign(n + 1, vector<int>());
for(int i=0;i<n-1;i++){
int u, v;
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
// 第一次 BFS找出u
vector<int> dist1 = bfs(1, n);
int u = 1;
for(int i=1;i<=n;i++) {
if(dist1[i] > dist1[u]) u = i;
}
// 第二次 BFS从u找出v并记录d1
vector<int> d1 = bfs(u, n);
int v = u;
for(int i=1;i<=n;i++) {
if(d1[i] > d1[v]) v = i;
}
// 第三次 BFS从v找出d2
vector<int> d2 = bfs(v, n);
// 输出每个节点的最远距离
for(int i=1;i<=n;i++) {
cout << max(d1[i], d2[i]) << (i==n ? '\n' : ' ');
}
}

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src/test.cpp Normal file
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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
struct TreeNode {
vector<int> children;
};
vector<TreeNode> tree;
vector<int> enjoyment;
vector<vector<long long>> dp;
void dfs(int u, int parent) {
dp[u][0] = 0;
dp[u][1] = enjoyment[u];
for (int v : tree[u].children) {
if (v == parent) continue;
dfs(v, u);
dp[u][0] += max(dp[v][0], dp[v][1]);
dp[u][1] += dp[v][0];
}
for (int v : tree[u].children) {
if (v == parent) continue;
long long option = dp[u][1] - dp[v][0] + dp[v][1] - b;
dp[u][1] = max(dp[u][1], option);
}
}
int main() {
int n, b;
cin >> n >> b;
enjoyment.resize(n + 1);
tree.resize(n + 1);
dp.resize(n + 1, vector<long long>(2));
for (int i = 1; i <= n; ++i) {
cin >> enjoyment[i];
}
for (int i = 0; i < n - 1; ++i) {
int x, y;
cin >> x >> y;
tree[x].children.push_back(y);
tree[y].children.push_back(x);
}
dfs(1, -1);
long long result = max(0LL, max(dp[1][0], dp[1][1]));
cout << result << endl;
return 0;
}