P1526

import java.util.LinkedList;
import java.util.Scanner;

public class Exercise1526 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int in;
		int[] a;

		while ((in = sc.nextInt()) != 0) {
			int sum = 0;
			int n = in;
			int m = sc.nextInt();
			DFSGraph g = new DFSGraph(n);
			for (int i = 0; i < m; i++)
				g.addEdge(sc.nextInt(), sc.nextInt());

			for (int i = 1; i <= n; i++)
				if (!g.marked[i]) {
					g.dfs(i);
					sum++;
				}
			System.out.println(sum);
		}
	}

	static class DFSGraph {

		int v;
		private boolean marked[];
		private LinkedList<Integer> node[];

		public DFSGraph(int v) {
			marked = new boolean[v + 1];
			node = (LinkedList<Integer>[]) new LinkedList[v + 1];
			for (int i = 1; i <= v; i++)
				node[i] = new LinkedList<Integer>();

		}

		private void addEdge(int s, int w) {
			node[s].add(w);
			node[w].add(s);
		}

		private void dfs(int s) {
			marked[s] = true;

			for (int w : node[s]) {
				while (!marked[w])
					dfs(w);
			}
		}
	}
}

深度遍歷求解，耗時過多

import java.io.IOException;
import java.util.Scanner;


public class Exercise1526_2 {


	static int[] a;
	static int[] sz;
	static int count;


	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		int in;
		while ((in = sc.nextInt()) != 0) {
			int n = in;


			int m = sc.nextInt();
			count = n;
			a = new int[n + 1];
			sz = new int[n + 1];
			for (int i = 1; i <= n; i++)
				a[i] = i;
			for (int i = 1; i <= n; i++)
				sz[i] = 1;


			for (int i = 0; i < m; i++) {


				int w = sc.nextInt();


				int v = sc.nextInt();
				union(w, v);


			}


			System.out.println(count);


		}
	}


	public static int find(int p) {
		while (a[p] != p)
			p = a[p];
		return p;


	}


	public static void union(int w, int v) {
		int idw = find(w);
		int idv = find(v);
		if (idw == idv)
			return;
		if (sz[idw] < sz[idv]) {
			a[idw] = idv;
			sz[idv] += sz[idw];
		} else {
			a[idv] = idw;
			sz[idw] += sz[idv];
		}


		count--;


	}
}

路徑壓縮的並查集法，總時間超時

import java.io.IOException;
import java.io.StreamTokenizer;
 
public class Exercise1526_3 {
 
    static int[] a;
    static int[] sz;
    static int count;
 
    public static void main(String[] args) throws IOException {
        StreamTokenizer st = new StreamTokenizer(System.in);
 
        while (st.nextToken() != StreamTokenizer.TT_EOF) {
            int n = (int) st.nval;
            if (n == 0)
                break;
            st.nextToken();
            int m = (int) st.nval;
            count = n;
            a = new int[n + 1];
            sz = new int[n + 1];
            for (int i = 1; i <= n; i++)
                a[i] = i;
            for (int i = 1; i <= n; i++)
                sz[i] = 1;
 
            for (int i = 0; i < m; i++) {
                st.nextToken();
                int w = (int) st.nval;
                st.nextToken();
                int v = (int) st.nval;
                union(w, v);
 
            }
 
            System.out.println(count);
 
        }
    }
 
    public static int find(int p) {
        while (a[p] != p)
            p = a[p];
        return p;
 
    }
 
    public static void union(int w, int v) {
        int idw = find(w);
        int idv = find(v);
        if (idw == idv)
            return;
        if (sz[idw] < sz[idv]) {
            a[idw] = idv;
            sz[idv] += sz[idw];
        } else {
            a[idv] = idw;
            sz[idw] += sz[idv];
        }
 
        count--;
 
    }
}

算法同2，換了IO方式（此IO方式已經過時）

import java.util.Scanner;


public class Exercise1529 {
	private static int[][] a;
	private static int[][] d;
	public static void main(String[] args)
	{
		Scanner sc = new Scanner(System.in);
		a=new int[9][9];
		while(sc.hasNext())
		{
			for(int i=1;i<=8;i++)
				for(int j=1;j<=8;j++)
					a[i][j]=sc.nextInt();
			d=new int[9][9];
			
			for(int i=1;i<=8;i++)
				for(int j=1;j<=8;j++)
					d[i][j]=Math.max(d[i-1][j], d[i][j-1])+a[i][j];
			System.out.println(d[8][8]);
		}
		
	}
}

微策略筆試，DP，最優子結構

d[i][j]=Math.max(d[i-1][j], d[i][j-1])+a[i][j];

P1532

import java.util.Scanner;

public class Exercise1532 {
	private static int[][] a;
	private static int limit;
	private static int max;
	private static boolean flag;

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		a = new int[9][9];
		while (sc.hasNext()) {
			limit = sc.nextInt();
			max = 0;
			flag = false;
			for (int i = 1; i <= 8; i++)
				for (int j = 1; j <= 8; j++)
					a[i][j] = sc.nextInt();
			dfs(1, 1, 0);
			if (flag)
				System.out.println(max);
			else
				System.out.println(-1);

		}
	}

	private static void dfs(int i, int j, int d) {
		d += a[i][j];
		if (d > limit)
			return;
		if (i == 8 && j == 8) {
			if (d > max) {
				max = d;
				flag = true;
			}
			return;
		}

		else if (i > 7)
			dfs(i, j + 1, d);
		else if (j > 7)
			dfs(i + 1, j, d);
		else {
			dfs(i, j + 1, d);
			dfs(i + 1, j, d);
		}
	}
}