HDU 1233 还是畅通工程 [最小生成树]

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Description

最小生成树

Algorithm

Kruskal算法

V1.0
用C++实现了 UnionFind类
不过用JAVA写这题就一直WA，不知如何是好

Prim算法

V2.0
JAVA没加优化，过了

Code

V2.0

import java.util.Arrays;import java.util.Scanner;public class Main {  public static void main(String[] args) {    final int INF = Integer.MAX_VALUE / 2;    Scanner cin = new Scanner(System.in);    for (;;) {      int n = cin.nextInt();      if (n == 0) break;      int m = n * (n - 1) / 2;      int[][] cost = new int[n][n];      for (int i = 0; i < n; i++) {        Arrays.fill(cost[i], INF);      }      for (int i = 0; i < m; i++) {        int a = cin.nextInt() - 1;        int b = cin.nextInt() - 1;        int c = cin.nextInt();        cost[a][b] = cost[b][a] = c;      }      int[] minCost = new int[n];      Arrays.fill(minCost, INF);      boolean[] used = new boolean[n];      Arrays.fill(used, false);      minCost[0] = 0;      int ans = 0;      for(;;) {        int v = -1;        for (int u = 0; u < n; u++) {          if (!used[u] && (v == -1 || minCost[u] < minCost[v])) v = u;        }        if (v == -1) break;        used[v] = true;        ans += minCost[v];        for (int u = 0; u < n; u++) {          minCost[u] = Math.min(minCost[u], cost[v][u]);        }      }      System.out.println(ans);    }  }}

V1.0

#include <cstdio>#include <algorithm>using namespace std;struct Edge{  int u, v, cost;};const int MAX_M = 109 * 108 / 2;const int MAX_N = 100 + 9;int n;bool comp(Edge a, Edge b){  if (a.cost < b.cost) return true; else return false;}struct UnionFind{  int n;  int par[MAX_N];  int rank[MAX_N];  UnionFind(int nn)  {    n = nn;    for (int i = 0; i < n; i++) {      par[i] = i;      rank[i] = i;    }  }  int find(int x)  {    if (par[x] == x) return x;    else return par[x] = find(par[x]);  }  void unite(int x, int y)  {    x = find(x);    y = find(y);    if (x == y) return;    if (rank[x] < rank[y]) {      par[x] = y;    } else {      par[y] = x;      if (rank[x] == rank[y]) rank[x]++;    }  }  bool same(int x, int y) {    return find(x) == find(y);  }  void print()  {    for (int i = 0; i < n; i++) {      printf("%d ", par[i]);    }  }  int total()  {    int s = 0;    for (int i = 0; i < n; i++) {      if (par[i] == i) s++;    }    return s;  }};void solve(){  int m = n * (n - 1) / 2;  Edge edges[MAX_M];  for (int i = 0; i < m; i++) {    scanf("%d%d%d", &edges[i].u, &edges[i].v, &edges[i].cost);  }  sort(edges, edges + m, comp);  UnionFind unionFind(n);  int ans = 0;  for (int i = 0; i < m; i++) {    if (!unionFind.same(edges[i].u - 1, edges[i].v - 1)) {      unionFind.unite(edges[i].u - 1, edges[i].v - 1);      ans += edges[i].cost;    }  }  printf("%d\n", ans);}int main(){  for (;;) {    scanf("%d", &n);    if (n == 0) break;    solve();  }}

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