【USACO 2017Feb】 Why Did the Cow Cross the Road

【题目链接】

点击打开链接

【算法】

dist[i][j][k]表示当前走到(i,j)，走的步数除以3的余数为k的最小花费

spfa即可

【代码】

#include<bits/stdc++.h>
using namespace std;
#define MAXN 110
const int INF = 1e9;

struct info
{
        int x,y,s;
};

const int dx[] = {,,-,};
const int dy[] = {-,,,};

int i,j,n,t;
int val[MAXN][MAXN];

template <typename T> inline void read(T &x)
{
    int f = ; x = ;
    char c = getchar();
    for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
    for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';
    x *= f;
}
template <typename T> inline void write(T x)
{
    if (x < )
    {
        putchar('-');
        x = -x;
    }
    if (x > ) write(x/);
    putchar(x%+'');
}
template <typename T> inline void writeln(T x)
{
    write(x);
    puts("");
}
bool ok(int x,int y)
{
        return x >=  && x <= n && y >=  && y <= n;
}
inline void spfa()
{
        int i,j,tx,ty,ans;
        queue< info > q;
        static int dist[MAXN][MAXN][],inq[MAXN][MAXN][];
        info cur;
        for (i = ; i <= n; i++)
        {
                for (j = ; j <= n; j++)
                {
                        dist[i][j][] = dist[i][j][] = dist[i][j][] = INF;
                }
        }
        dist[][][] = ;
        inq[][][] = ;
        q.push((info){,,});
        while (!q.empty())
        {
                cur = q.front();
                inq[cur.x][cur.y][cur.s] = ;
                q.pop();
                for (i = ; i < ; i++)
                {
                        tx = cur.x + dx[i];
                        ty = cur.y + dy[i];
                        if (ok(tx,ty))
                        {
                                if (!cur.s)
                                {
                                        if (dist[cur.x][cur.y][] + t < dist[tx][ty][])
                                        {
                                                dist[tx][ty][] = dist[cur.x][cur.y][] + t;
                                                if (!inq[tx][ty][])
                                                {
                                                        inq[tx][ty][] = ;
                                                        q.push((info){tx,ty,});
                                                }
                                        }
                                }
                                if (cur.s == )
                                {
                                        if (dist[cur.x][cur.y][] + t < dist[tx][ty][])
                                        {
                                                dist[tx][ty][] = dist[cur.x][cur.y][] + t;
                                                if (!inq[tx][ty][])
                                                {
                                                        inq[tx][ty][] = ;
                                                        q.push((info){tx,ty,});
                                                }
                                        }
                                }
                                if (cur.s == )
                                {
                                        if (dist[cur.x][cur.y][] + val[tx][ty] + t < dist[tx][ty][])
                                        {
                                                dist[tx][ty][] = dist[cur.x][cur.y][] + val[tx][ty] + t;
                                                if (!inq[tx][ty][])
                                                {
                                                        inq[tx][ty][] = ;
                                                        q.push((info){tx,ty,});
                                                }
                                        }
                                }
                        }
                }
        }
        ans = min(min(dist[n][n][],dist[n][n][]),dist[n][n][]);
        writeln(ans);
}

int main() {

        read(n); read(t);

        for (i = ; i <= n; i++)
        {
                for (j = ; j <= n; j++)
                {
                        read(val[i][j]);
                }
        }
        spfa();

        return ;

}