[代码]ural 1655 Somali Pirates

Abstract

ural 1655 Somali Pirates

dp

Source

http://acm.timus.ru/problem.aspx?space=1&num=1655

Solution

dp水题，但是我3y，所以不算水题。

Code

#include <cassert>

#include <iostream>

#include <cmath>

#include <cstdio>

#include <cstring>

#include <algorithm>

using namespace std;



const double EPS = 1e-6;

const double INF = 1e8;



double da, w;

int N;

bool vis[555][555][2];

double f[555][555][2];

int path[555][555][2];



struct snode {

    int id;

    double a, t;

    void read(int i) {

        id = i;

        double d, v;

        cin>>a>>d>>v;

        a -= da;

        if (a<-EPS) a += 360;

        t = (d-1)/v*60;

    }

    bool operator<(const snode &rhs) const {

        return a<rhs.a;

    }

}node[555];



inline double cost(int i, int j) {

    return min(360-fabs(node[i].a-node[j].a),

            fabs(node[i].a-node[j].a))/w;

}



double dfs(int i, int j, int d) {

    if (vis[i][j][d]) return f[i][j][d];

    f[i][j][d] = INF;

    vis[i][j][d] = 1;

    if (i==0&&d==0 || j==N+1&&d==1) return f[i][j][d];

    if (d==0) {

        double t = dfs(i-1, j, 0)+cost(i-1, i);

        if (t<node[i].t+EPS && t<f[i][j][d]-EPS) {

            f[i][j][d] = t;

            path[i][j][d] = 0;

        }

        t = dfs(i-1, j, 1)+cost(j, i);

        if (t<node[i].t+EPS && t<f[i][j][d]-EPS) {

            f[i][j][d] = t;

            path[i][j][d] = 1;

        }

    }

    else {

        double t = dfs(i, j+1, 1)+cost(j, j+1);

        if (t<node[j].t+EPS && t<f[i][j][d]-EPS) {

            f[i][j][d] = t;

            path[i][j][d] = 1;

        }

        t = dfs(i, j+1, 0)+cost(i, j);

        if (t<node[j].t+EPS && t<f[i][j][d]-EPS) {

            f[i][j][d] = t;

            path[i][j][d] = 0;

        }

    }

    return f[i][j][d];

}



void write(int i, int j, int d, int dep) {

    if (dep==N) return;

    if (d) write(i, j+1, path[i][j][d], dep+1);

    else write(i-1, j, path[i][j][d], dep+1);

    printf("%d\n", d?node[j].id:node[i].id);

}



int main() {

    int i, j, k;

    while (cin>>da>>w>>N) {

        w *= 360; //degree per minute

        for (i = 1; i <= N; ++i)

            node[i].read(i);

        sort(node+1, node+N+1);

        node[0].a = 0, node[N+1].a = 360;

        memset(vis, 0, sizeof vis);

        f[0][N+1][0] = f[0][N+1][1] = 0;

        vis[0][N+1][0] = vis[0][N+1][1] = 1;

        int ansi, ansd;

        double ans = INF;

        for (i = 0; i <= N; ++i)

            for (k = 0; k < 2; ++k) {

                if (dfs(i, i+1, k)<ans-EPS) {

                    ans = dfs(i, i+1, k);

                    ansi = i;

                    ansd = k;

                }

            }

        if (ans < 1e6) {

            printf("%f\n", ans);

            write(ansi, ansi+1, ansd, 0);

        }

        else puts("Impossible");

    }

    return 0;

}