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55 lines
1.4 KiB
55 lines
1.4 KiB
#include <bits/stdc++.h>
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using namespace std;
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const int N = 510;
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const int INF = 0x3f3f3f3f;
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int n, m;
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int g[N][N]; // 稠密图，邻接矩阵
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int dis[N]; // 这个点到集合的距离
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bool st[N]; // 是不是已经使用过
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int res; // 最小生成树里面边的长度之和
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int pre[N]; // 前驱结点
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// 普利姆算法求最小生成树
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int prim() {
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memset(dis, 0x3f, sizeof dis);
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memset(pre, -1, sizeof pre); // 记录前驱路径
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dis[1] = 0;
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for (int i = 0; i < n; i++) { // 迭代n次
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int t = -1;
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for (int j = 1; j <= n; j++)
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if (!st[j] && (t == -1 || dis[t] > dis[j])) t = j;
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if (i && dis[t] == INF) return INF; // 非连通图，没有最小生成树
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if (i) res += dis[t];
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for (int j = 1; j <= n; j++)
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if (!st[j] && g[t][j] < dis[j]) {
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dis[j] = g[t][j];
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pre[j] = t; // 记录是由谁转移而来
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}
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st[t] = true;
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}
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return res;
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}
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int main() {
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cin >> n >> m;
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memset(g, 0x3f, sizeof g);
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// 读入数据
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while (m--) {
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int a, b, c;
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cin >> a >> b >> c;
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g[a][b] = g[b][a] = min(g[a][b], c);
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}
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int t = prim();
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if (t == INF)
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puts("impossible");
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else
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cout << t << endl;
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// 输出前驱结点
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for (int i = 1; i <= n; i++) printf("%d ", pre[i]);
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return 0;
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} |