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55 lines
1.3 KiB
55 lines
1.3 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 dist[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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/**
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* 功能：普利姆算法求最小生成树
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* @return
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*/
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int prim() {
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// 迭代n次
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for (int i = 0; i < n; i++) {
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// 找出距离集合最小的点
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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 || dist[t] > dist[j])) t = j;
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// 如果找不到距离最小的点
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if (i && dist[t] == INF) return INF;
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// 累加最小生成树的长度
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if (i) res += dist[t];
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// 利用找到的t更新其它的点
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for (int j = 1; j <= n; j++)
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if (!st[j] && g[t][j] < dist[j])
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dist[j] = g[t][j];
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// 标识t点已在集合内
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st[t] = 1;
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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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memset(dist, 0x3f, sizeof dist);
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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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printf("%d\n", t);
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return 0;
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}
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