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Frogger

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用户1147447
发布2019-05-26 00:15:59
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发布2019-05-26 00:15:59
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文章被收录于专栏:机器学习入门

POJ 刷题系列:2253. Frogger

题意:

湖里有各个石头的坐标,Freddy能够借助石头跳跃到Fiona的每条路径中的最大跳跃距离的最小值。

思路: 以为是二分+dfs,会超时。与其这样还不如直接dfs每条路径求出max的同时,抵达终点时求min,结果还是超时。想了下,难道可以用DP做状态记录,所以借用floyd算法的思路,经过N轮,对于每个点(石头)存在两种情况,要么经过它,要么不经过它。所以DP更新式如下:

代码语言:javascript
复制
dp[i][j][k] = min(dp[i][j][k - 1], max(dp[i][k][k-1], dp[k][j][k-1]))

代码如下:

代码语言:javascript
复制
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Map;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201712/P2253.txt";

    public static void main(String[] args) throws IOException {
        new Main().run();
    }

    int N;
    double maxDist;
    double[][] dist;

    double dist(int x1, int y1, int x2, int y2) {
        double dx = x1 - x2;
        double dy = y1 - y2;
        return Math.sqrt(dx * dx + dy * dy);
    }

    void read() {
        int T = 1;
        while (true) {
            N = ni();
            if (N == 0) break;
            int[][] points = new int[N][2];
            for (int i = 0; i < N; ++i) {
                int x = ni();
                int y = ni();
                points[i] = new int[] {x, y};
            }

            dist = new double[N][N];
            maxDist = 0;
            for (int i = 0; i < N; ++i) {
                for (int j = i; j < N; ++j) {
                    if (i == j) {
                        dist[i][j] = 0;
                    }
                    else {
                        dist[i][j] = dist[j][i] = dist(points[i][0], points[i][1], points[j][0], points[j][1]);
                        maxDist = Math.max(maxDist, dist[i][j]);
                    }
                }
            }

            for (int k = 0; k < N; ++k) {
                for (int i = 0; i < N; ++i) {
                    for (int j = 0; j < N; ++j) {
                        dist[i][j] = Math.min(dist[i][j], Math.max(dist[i][k], dist[k][j]));
                    }
                }
            }

            out.println("Scenario #" + T);
            out.printf("Frog Distance = %.3f\n", dist[0][1]);
            out.println();
            T++;
        }
    }

    FastScanner in;
    PrintWriter out;

    void run() throws IOException {
        boolean oj;
        try {
            oj = ! System.getProperty("user.dir").equals("F:\\oxygen_workspace\\Algorithm");
        } catch (Exception e) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
        }

        InputStream is = oj ? System.in : new FileInputStream(new File(INPUT));
        in = new FastScanner(is);
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        read();
        out.flush();
        if (!oj){
            System.out.println("[" + (System.currentTimeMillis() - s) + "ms]");
        }
    }

    public boolean more(){
        return in.hasNext();
    }

    public int ni(){
        return in.nextInt();
    }

    public long nl(){
        return in.nextLong();
    }

    public double nd(){
        return in.nextDouble();
    }

    public String ns(){
        return in.nextString();
    }

    public char nc(){
        return in.nextChar();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;
        boolean hasNext;

        public FastScanner(InputStream is) throws IOException {
            br = new BufferedReader(new InputStreamReader(is));
            hasNext = true;
        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (Exception e) {
                    hasNext = false;
                    return "##";
                }
            }
            return st.nextToken();
        }

        String next = null;
        public boolean hasNext(){
            next = nextToken();
            return hasNext;
        }

        public int nextInt() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Integer.parseInt(more);
        }

        public long nextLong() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Long.parseLong(more);
        }

        public double nextDouble() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Double.parseDouble(more);
        }

        public String nextString(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more;
        }

        public char nextChar(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more.charAt(0);
        }
    }

    static class D{

        public static void pp(int[][] board, int row, int col) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < row; ++i) {
                for (int j = 0; j < col; ++j) {
                    sb.append(board[i][j] + (j + 1 == col ? "\n" : " "));
                }
            }
            System.out.println(sb.toString());
        }

        public static void pp(char[][] board, int row, int col) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < row; ++i) {
                for (int j = 0; j < col; ++j) {
                    sb.append(board[i][j] + (j + 1 == col ? "\n" : " "));
                }
            }
            System.out.println(sb.toString());
        }
    }

    static class ArrayUtils {

        public static void fill(int[][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                Arrays.fill(f[i], value);
            }
        }

        public static void fill(int[][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }

        public static void fill(int[][][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }
    }

    static class Num{
        public static <K> void inc(Map<K, Integer> mem, K k) {
            if (!mem.containsKey(k)) mem.put(k, 0);
            mem.put(k, mem.get(k) + 1);
        }
    }
}
这里写图片描述
这里写图片描述
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原始发表:2017年12月27日,如有侵权请联系 cloudcommunity@tencent.com 删除

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