alg2025/src/9/25/P8817.cpp
Zengtudor 66f957900f refactor(P8817): 重构题目解法并优化性能
将原递归实现改为BFS算法计算节点间距离
使用预处理和剪枝优化计算效率
添加完整解题逻辑计算最大得分
2025-09-25 15:43:14 +08:00

100 lines
2.0 KiB
C++

#include <algorithm>
#include <iostream>
#include <queue>
#include <vector>
using ll = long long;
const int MAXN = 2505;
int n;
int m;
int k;
ll sc[MAXN];
std::vector<int> adj[MAXN];
int dist[MAXN][MAXN];
std::vector<int> pre[MAXN];
void bfs(int s) {
std::queue<std::pair<int, int>> q;
q.push({s, 0});
dist[s][s] = 0;
while (!q.empty()) {
auto [u, d] = q.front();
q.pop();
if (d > k) {
continue;
}
for (int v : adj[u]) {
if (dist[s][v] == -1) {
dist[s][v] = d + 1;
q.push({v, d + 1});
}
}
}
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cin >> n >> m >> k;
for (int i = 2; i <= n; ++i) {
std::cin >> sc[i];
}
for (int i = 0; i < m; ++i) {
int u, v;
std::cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
for (int i = 1; i <= n; ++i) {
for (int j = 1; j <= n; ++j) {
dist[i][j] = -1;
}
}
for (int i = 1; i <= n; ++i) {
bfs(i);
}
for (int i = 2; i <= n; ++i) {
for (int j = 2; j <= n; ++j) {
if (i == j)
continue;
if (dist[1][j] != -1 && dist[j][i] != -1) {
pre[i].push_back(j);
}
}
std::sort(pre[i].begin(), pre[i].end(), [&](int a, int b) { return sc[a] > sc[b]; });
if (pre[i].size() > 3) {
pre[i].resize(3);
}
}
ll ans = 0;
for (int b = 2; b <= n; ++b) {
for (int c = 2; c <= n; ++c) {
if (b == c)
continue;
if (dist[b][c] != -1) {
for (int a : pre[b]) {
for (int d : pre[c]) {
if (a != c && a != d && b != d) {
ans = std::max(ans, sc[a] + sc[b] + sc[c] + sc[d]);
}
}
}
}
}
}
std::cout << ans << std::endl;
}