[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;
}