【BZOJ 1295】 [SCOI2009]最长距离

#include <bits/stdc++.h>
#define LL long long
#define rep1(i,a,b) for (int i = a;i <= b;i++)
#define rep2(i,a,b) for (int i = a;i >= b;i--)
#define all(x) x.begin(),x.end()
#define pb push_back
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
using namespace std;

const double pi = acos(-1);
const int dx[4] = {0,0,1,-1};
const int dy[4] = {1,-1,0,0};
const int N = 30;

int n,m,t,dis[N*N+10][N*N+10];;
vector<pair<int,int> > g[N*N+10];
char s[N+10][N+10];
queue<int> dl;
bool inq[N*N+10];

void deal_with(int x,int y){
    memset(inq,0,sizeof inq);
    int S = (x-1)*m+y;
    memset(dis[S],255,sizeof dis[S]);
    dis[S][S] = s[x][y]-'0';
    dl.push(S);
    inq[S] = true;
    while (!dl.empty()){
        int x = dl.front();dl.pop();
        inq[x] = false;
        for (int i = 0;i < (int)g[x].size();i++){
            int y = g[x][i].first,cost = g[x][i].second;
            if (dis[S][y]==-1 || dis[S][y]>dis[S][x]+cost) {
                dis[S][y] = dis[S][x]+cost;
                if (!inq[y]){
                    inq[y] = true;
                    dl.push(y);
                }
            }

        }
    }
}

double sqr(double x){
    return x*x;
}

int main(){
    #ifdef LOCAL_DEFINE
        freopen("rush_in.txt", "r", stdin);
    #endif
    ios::sync_with_stdio(0),cin.tie(0);
    cin >> n >> m >> t;
    rep1(i,1,n) cin >> (s[i]+1);
    rep1(i,1,n)
        rep1(j,1,m)
            rep1(k,0,3){
                int tx = i + dx[k],ty = j+dy[k];
                if (tx>=1 && tx<= n && ty>=1 && ty<=m){
                    int x = (i-1)*m+j,y = (tx-1)*m+ty;
                    g[x].push_back(make_pair(y,s[tx][ty]-'0'));
                }
            }
    rep1(i,1,n)
        rep1(j,1,m)
            deal_with(i,j);

    double ans = 0;
    rep1(i,1,n)
        rep1(j,1,m)
            rep1(ii,1,n)
                rep1(jj,1,m){
                    int x = (i-1)*m+j,y = (ii-1)*m+jj;
                    if (dis[x][y]<=t){
                        ans = max(ans,sqrt(sqr(ii-i)+sqr(jj-j)));
                    }
                }
    cout<<fixed<<setprecision(6)<<ans<<endl;
    return 0;
}