[BJOI2006] 狼抓兔子

http://www.lydsy.com/JudgeOnline/problem.php?id=1001

#include <cstdio>
#include <algorithm>
#include <queue>
#include <cmath>
#include <cstring>
#include <iostream>

using namespace std;
const int N = 2001000;

#define inf 999999999
#define gc getchar()

struct G{
    int v, nxt, w;
}G[N << 2];
int n, m, ans, num, S, T, head[N], dis[N];
bool vis[N];
queue <int> Q;
 
inline int read(){
    int x = 0, f = 1; char c = gc;
    while(c < '0' || c > '9') {if(c == '-') f = -1; c = gc;} 
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = gc;
    return x * f;
}
 
void add(int u, int v, int w){
    G[++num].v = v; G[num].w = w;
    G[num].nxt = head[u]; head[u] = num;
}
 
inline void spfa(){
    for(int i = S; i <= T; i ++) dis[i] = inf, vis[i] = 0;
    dis[S] = 0;
    Q.push(S);
    while(!Q.empty()){
        int topp = Q.front();
        Q.pop();
        vis[topp] = 0;
        for(int i = head[topp]; i; i = G[i].nxt){
            int v = G[i].v;
            if(dis[v] > dis[topp] + G[i].w){
                dis[v] = dis[topp] + G[i].w;
                if(!vis[v]) vis[v] = 1, Q.push(v);
            }
        }
    }
    ans = dis[T];
}

inline void build(){
    S = 0, T = ((n - 1) * (m - 1)) << 1 | 1;
    for(int i = 1; i <= n; i ++)
        for(int j = 1; j < m;  j++){
            int x = read(), u, v;
            if (i == 1) u = S, v = j;
            else if (i == n) u = ((i - 2) << 1 | 1) * (m - 1) + j, v = T;
            else u = ((i - 2) << 1 | 1) * (m - 1) + j, v = ((i - 1) << 1) * (m - 1) + j;
            add(u, v, x), add(v, u, x);
        }
    for(int i = 1; i < n; i ++)
        for(int j = 1; j <= m; j ++){
            int x = read(), u, v;
            if (j == 1) u = ((i - 1) << 1 | 1) * (m - 1) + 1, v = T;
            else if (j == m) u = S, v = ((i - 1) << 1 | 1) * (m - 1);
            else u = ((i - 1) << 1) * (m - 1) + j - 1, v = ((i - 1) << 1 | 1) * (m - 1) + j;
            add(u, v, x), add(v, u, x);
        }
    for(int i=1; i<n; i++)
        for(int j=1; j<m; j++){
            int x = read(), u, v;
            u = ((i - 1) << 1) * (m - 1) + j, v = ((i - 1) << 1 | 1) * (m - 1) + j;
            add(u, v, x), add(v, u, x);
        }
}
 
int main()
{
    n = read(), m = read(); 
    build();
    spfa();
    printf("%d
",ans);
    return 0;
}