hdu 3329 The Flood (Flood Fill + MFSet)

Problem - 3329

　　用pfs，将淹没时间调整回来，然后用并查集，时间倒序插入点。

代码如下：

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

 using namespace std;

 const int N = ;
 const int dx[] = { -, , , };
 const int dy[] = { , -, , };
 bool vis[N][N];
 int mat[N][N];

 typedef pair<int, int> PII;
 typedef pair<int, PII> PIII;
 priority_queue<PIII> pq;
 int n, m;
 inline bool inmat(int x, int y) { return  <= x && x < n &&  <= y && y < m;}

 void adjust() {
     int ht, cx, cy, nx, ny;
     while (!pq.empty()) {
         PIII tmp = pq.top();
         pq.pop();
         ht = -tmp.first, cx = tmp.second.first, cy = tmp.second.second;
         //cout << ht << ' ' << cx << ' ' << cy << endl;
         for (int i = ; i < ; i++) {
             nx = cx + dx[i], ny = cy + dy[i];
             if (!inmat(nx, ny)) continue;
             if (vis[nx][ny]) continue;
             mat[nx][ny] = max(ht, mat[nx][ny]);
             pq.push(PIII(-mat[nx][ny], PII(nx, ny)));
             vis[nx][ny] = true;
         }
     }
     //for (int i = 0; i < n; i++) {
         //for (int j = 0; j < m; j++) cout << mat[i][j] << ' ';
         //cout << endl;
     //}
 }

 struct MFS {
     int fa[N * N];
     void init() { for (int i = ; i < N * N; i++) fa[i] = i;}
     int find(int x) { return fa[x] = fa[x] == x ? x : find(fa[x]);}
     bool merge(int x, int y) {
         int fx = find(x), fy = find(y);
         if (fx == fy) return false;
         fa[fx] = fy;
         return true;
     }
 } mfs;

 int work() {
     int ret = -;
     for (int i = ; i < n; i++) {
         for (int j = ; j < m; j++) {
             pq.push(PIII(mat[i][j], PII(i, j)));
             mat[i][j] = -;
         }
     }
     PIII tmp;
     int nid = , mg = , nx, ny;
     bool sp = false;
     mfs.init();
     while (!pq.empty()) {
         int ct = pq.top().first;
         while (!pq.empty() && ct == pq.top().first) {
             tmp = pq.top();
             int h = tmp.first, x = tmp.second.first, y = tmp.second.second;
             pq.pop();
             mat[x][y] = nid++;
             for (int i = ; i < ; i++) {
                 nx = x + dx[i], ny = y + dy[i];
                 if (!inmat(nx, ny)) continue;
                 if (mat[nx][ny] == -) continue;
                 mg += mfs.merge(mat[x][y], mat[nx][ny]);
             }
         }
         if (sp) {
             if (mg == nid - ) ret = ct, sp = false;
         } else {
             if (mg != nid - ) sp = true;
         }
     }
     return ret;
 }

 int main() {
     int cas = ;
        while (~scanf("%d%d", &n, &m) && (n || m)) {
         while (!pq.empty()) pq.pop();
         memset(vis, , sizeof(vis));
         for (int i = ; i < n; i++) {
             for (int j = ; j < m; j++) {
                 scanf("%d", &mat[i][j]);
                 if (i ==  || i == n -  || j ==  || j == m - ) {
                     pq.push(PIII(-mat[i][j], PII(i, j)));
                     vis[i][j] = true;
                 }
             }
         }
         //cout << "??" << endl;
         adjust();
         int ans = work();
         if (ans == -) printf("Case %d: Island never splits.\n", cas++);
         else printf("Case %d: Island splits when ocean rises %d feet.\n", cas++, ans);
     }
     return ;
 }

——written by Lyon