牛客国庆集训派对Day1 B. Attack on Titan

B. Attack on Titan

链接

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
#include<cmath>
#include<cctype>
#include<set>
#include<queue>
#include<vector>
#include<map>
using namespace std;
typedef long long LL;

inline int read() {
    int x=,f=;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-;
    for(;isdigit(ch);ch=getchar())x=x*+ch-'';return x*f;
}

const int N = ;
const double g2 = sqrt(2.0), INF = 1e18, eps = 1e-;
int dx[] = {, , -, , , , -, -};
int dy[] = {, -, , , -, , -, };
int nxt1[], nxt2[];
bool vis[N][N][];
double A[N][N], dis[N][N][], w[];

struct Node{
    int x, y, now; double dis;
    bool operator < (const Node &A) const { return dis > A.dis; }
}tmp[];
priority_queue< Node >q;

int main() {
    int n = read(), m = read(), C = read(), cnt = ;
    for (int i = ; i <= n; ++i)
        for (int j = ; j <= m; ++j) A[i][j] = read();
    for (int i = -; i <= ; ++i)
        for (int j = -; j <= ; ++j) {
            double v = i + j * g2;
            if (v >=  && v <= C) w[++cnt] = v;
        }
    sort(w + , w + cnt + );
    for (int i = ; i <= cnt; ++i) {
        for (int j = i - ; ~j; --j) if (fabs(w[i] - w[j] - ) < eps) { nxt1[i] = j; break; }
        for (int j = i - ; ~j; --j) if (fabs(w[i] - w[j] - g2) < eps) { nxt2[i] = j; break; }
    }
    for (int i = ; i <= n; ++i)
        for (int j = ; j <= m; ++j)
            for (int k = ; k <= cnt; ++k) dis[i][j][k] = INF;
    dis[][][] = , q.push((Node){, , , });
    while (!q.empty()) {
        Node topp = q.top(); q.pop();
        int x = topp.x, y = topp.y, now = topp.now;
        if (vis[x][y][now]) continue;
        if (x == n && y == m) { printf("%.10lf",dis[x][y][now]); return ; }
        vis[x][y][now] = ;
        int t = ;
        if (w[now] + eps > ) {
            for (int i = ; i < ; ++i) {
                int nx = x + dx[i], ny = y + dy[i];
                if (nx >=  && nx <= n && ny >=  && ny <= m) tmp[++t] = (Node){nx,ny,nxt1[now],};
            }
        }
        if (w[now] + eps > g2) {
            for (int i = ; i < ; ++i) {
                int nx = x + dx[i], ny = y + dy[i];
                if (nx >=  && nx <= n && ny >=  && ny <= m) tmp[++t] = (Node){nx,ny,nxt2[now],};
            }
        }
        double d = dis[x][y][now];
        if(now<cnt) tmp[++t]=(Node){x,y,now+,(w[now+]-w[now])*A[x][y]};
        for (int i = ; i <= t; ++i) {
            if (dis[tmp[i].x][tmp[i].y][tmp[i].now] > d + tmp[i].dis)
                dis[tmp[i].x][tmp[i].y][tmp[i].now] = tmp[i].dis = d + tmp[i].dis, q.push(tmp[i]);
        }
    }
    return ;
}