POJ 1258

Prim算法：

• import java.io.*;
  import java.util.*;
  import java.math.*;
  import java.text.*;
  
  public classMain {
  	
  	static final int MAXN = 105;
  	static final int MAXM = 20005;
  	static final int MOD = 10000;
  	static final int INF = 1000000000;
  	static final double EPS = 1E-6;
  	
  	int n, q, a, b;
  	int[][] g = new int[MAXN][MAXN];
  	boolean[] vis = new boolean[MAXN];
  	int[] dis = new int[MAXN];
  	
  	void init() {
  		
  	}
  	
  	int Prim() {
  		for (int i = 1; i <= n; i++) {
  			vis[i] = false;
  			dis[i] = INF;
  		}
  		dis[1] = 0;
  		int sum = 0;
  		for (int i = 1; i <= n; i++) {
  			int k = -1;
  			for (int j = 1; j <= n; j++) {
  				if (vis[j] == false && (k == -1 || dis[j] < dis[k]))
  					k = j;
  			}
  			sum += dis[k];
  			vis[k] = true;
  			for (int j = 1; j <= n; j++) {
  				if (vis[j] == false && g[k][j] < dis[j]) 
  					dis[j] = g[k][j];
  			}
  		}
  		return sum;
  	}
  	
  	void run() {
  		while (cin.hasNext()) {
  			n = cin.nextInt();
  			for (int i = 1; i <= n; i++) {
  				for (int j = 1; j <= n; j++) {
  					g[i][j] = cin.nextInt();
  				}
  			}
  			System.out.println(Prim());
  		}
  	}	
  
  	public static void main(String[] args) {
  		Main solved = new Main();
  		solved.run();
  	}
  	
  	Scanner cin = new Scanner(new BufferedInputStream(System.in));
  
  }

 

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Kruskal算法：

 

• import java.io.*;
  import java.util.*;
  import java.math.*;
  import java.text.*;
  
  public classMain {
  	
  	static final int MAXN = 105;
  	static final int MAXM = 5005;
  	static final int MOD = 10000;
  	static final int INF = 1000000000;
  	static final double EPS = 1E-6;
  	
  	int n, es, x;
  	int[] f = new int[MAXN];
  	Edge[] edge = new Edge[MAXM];
  	
  	void init() {
  		es = 0;
  		for (int i = 1; i <= n; i++) 
  			f[i] = i;
  	}
  	
  	int find(int x) {
  		if (x != f[x]) 
  			f[x] = find(f[x]);
  		return f[x];
  	}
  	
  	boolean Union(int x, int y) {
  		x = find(x); y = find(y);
  		if (x == y) return false;
  		f[x] = y;
  		return true;
  	}
  	
  	int Kruskal() {
  		int ans, j;
  		ans = j = 0;
  		for (int i = 0; i < es && j < n - 1; i++) {
  			if (Union(edge[i].u, edge[i].v) == false) continue;
  			ans += edge[i].w;
  			j++;
  		}
  		return ans;
  	}
  	
  	void run() {
  		while (cin.hasNext()) {
  			n = cin.nextInt();
  			init();
  			for (int i = 1; i <= n; i++) {
  				for (int j = 1; j <= n; j++) {
  					x = cin.nextInt();
  					if (i < j) {
  						edge[es++] = new Edge(i, j, x);
  					}
  				}
  			}
  			Arrays.sort(edge, 0, es);
  			System.out.println(Kruskal());
  		}
  	}	
  
  	public static void main(String[] args) {
  		Main solved = new Main();
  		solved.run();
  	}
  	
  	Scanner cin = new Scanner(new BufferedInputStream(System.in));
  
  }
  
  classEdge implements Comparable<Edge> {
  	int u, v, w;
  	
  	Edge() {}
  	
  	Edge(int u, int v, int w) {
  		this.u = u;
  		this.v = v;
  		this.w = w;
  	}
  	
  	public int compareTo(Edge e) {
  		return this.w - e.w;
  	}
  }

 

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两者用的都是贪心，生成树不唯一。

注意Java的比较函数的写法。