五项一起对得上吗
运行下面这段程序:
#include <algorithm>
#include <iostream>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
const ll INF = 1000000000; // 走不到的点记这个值,输出时写成 -1
using Graph = vector<vector<pair<int, int>>>; // g[u] 里放 (邻居 v, 边权 w)
// 七个点的无向图(和 Python 版同一组数据):0-1:2 0-2:1 1-3:3 2-4:9 3-4:1 5-6:7
const vector<vector<int>> E7 = {{0, 1, 2}, {0, 2, 1}, {1, 3, 3}, {2, 4, 9}, {3, 4, 1}, {5, 6, 7}};
// 主连通块五个点、五条边(求最小生成树用)
const vector<vector<int>> E5 = {{0, 1, 2}, {0, 2, 1}, {1, 3, 3}, {2, 4, 9}, {3, 4, 1}};
// 有向负权反例:0→1:4 0→2:5 2→1:-3 1→3:1
const Graph NEG = {{{1, 4}, {2, 5}}, {{3, 1}}, {{1, -3}}, {}};
// 同一张图,只把 2→1 那条边改成 +3
const Graph POS = {{{1, 4}, {2, 5}}, {{3, 1}}, {{1, 3}}, {}};
// 有负环:0→1:1 1→2:-1 2→1:-1
const Graph CYC = {{{1, 1}}, {{2, -1}}, {{1, -1}}};
Graph build(int n, const vector<vector<int>>& edges) {
// 无向图:每条边 {a, b, w} 两个方向都加;邻接表按邻居编号排好
Graph g(n);
for (const auto& e : edges) {
g[e[0]].push_back({e[1], e[2]});
g[e[1]].push_back({e[0], e[2]});
}
for (auto& adj : g) sort(adj.begin(), adj.end());
return g;
}
vector<ll> dijkstra(const Graph& g, int s) {
vector<ll> d(g.size(), INF);
vector<bool> done(g.size(), false);
// 小根堆:greater 让距离小的先出(不写就是大根堆)
priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> pq;
d[s] = 0;
pq.push({0, s});
while (!pq.empty()) {
auto [du, u] = pq.top();
pq.pop();
if (done[u]) continue;
done[u] = true;
for (auto [v, w] : g[u]) {
if (du + w < d[v]) {
d[v] = du + w;
pq.push({d[v], v});
}
}
}
return d;
}
vector<ll> bellman(const Graph& g, int s) {
int n = g.size();
vector<ll> d(n, INF);
d[s] = 0;
for (int round = 0; round < n - 1; round++) {
for (int u = 0; u < n; u++) {
if (d[u] == INF) continue;
for (auto [v, w] : g[u]) {
if (d[u] + w < d[v]) d[v] = d[u] + w;
}
}
}
return d;
}
vector<int> make_set(int n) {
vector<int> p(n);
for (int i = 0; i < n; i++) p[i] = i;
return p;
}
int find_root(vector<int>& p, int x) {
while (p[x] != x) {
p[x] = p[p[x]]; // 路径压缩:挂到爷爷上
x = p[x];
}
return x;
}
bool unite(vector<int>& p, int a, int b) {
// 两端已在同一块里就返回 false(这条边会成环)
int ra = find_root(p, a), rb = find_root(p, b);
if (ra == rb) return false;
p[ra] = rb;
return true;
}
struct MST {
ll total;
vector<pair<int, int>> picked;
};
MST kruskal(int n, vector<vector<int>> edges) {
// 按 (权重, 两端编号) 从小到大排,union 成功才要这条边
sort(edges.begin(), edges.end(), [](const vector<int>& x, const vector<int>& y) {
if (x[2] != y[2]) return x[2] < y[2];
if (x[0] != y[0]) return x[0] < y[0];
return x[1] < y[1];
});
vector<int> p = make_set(n);
MST r{0, {}};
for (const auto& e : edges) {
if (unite(p, e[0], e[1])) {
r.total += e[2];
r.picked.push_back({e[0], e[1]});
}
}
return r;
}
MST prim(int n, const vector<vector<int>>& edges, int s) {
vector<vector<pair<int, int>>> ad(n); // ad[u] 里放 (w, x)
for (const auto& e : edges) {
ad[e[0]].push_back({e[2], e[1]});
ad[e[1]].push_back({e[2], e[0]});
}
vector<bool> seen(n, false);
seen[s] = true;
// 堆里放 (权重, 树里那端, 树外那端),权重小的先出
priority_queue<tuple<int, int, int>, vector<tuple<int, int, int>>, greater<tuple<int, int, int>>> pq;
for (auto [w, v] : ad[s]) pq.push({w, s, v});
MST r{0, {}};
int cnt = 1;
while (!pq.empty() && cnt < n) {
auto [w, u, v] = pq.top();
pq.pop();
if (seen[v]) continue;
seen[v] = true;
cnt++;
r.total += w;
r.picked.push_back({u, v});
for (auto [w2, x] : ad[v]) {
if (!seen[x]) pq.push({w2, v, x});
}
}
return r;
}
int main() {
Graph g = build(7, E7);
bool ok = dijkstra(g, 0)[4] == 6 && dijkstra(NEG, 0)[3] == 5 && bellman(NEG, 0)[3] == 3
&& kruskal(5, E5).total == 7 && prim(5, E5, 0).total == 7;
cout << boolalpha << ok << endl;
}
(本题用 g++ -std=c++17 -O0 编译。)
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