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 = 111;
const int dx[4] = { -1, 0, 1, 0};
const int dy[4] = { 0, -1, 0, 1};
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 0 <= x && x < n && 0 <= 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 = 0; i < 4; 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 = 0; 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 = -1;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            pq.push(PIII(mat[i][j], PII(i, j)));
            mat[i][j] = -1;
        }
    }
    PIII tmp;
    int nid = 0, mg = 0, 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 = 0; i < 4; i++) {
                nx = x + dx[i], ny = y + dy[i];
                if (!inmat(nx, ny)) continue;
                if (mat[nx][ny] == -1) continue;
                mg += mfs.merge(mat[x][y], mat[nx][ny]);
            }
        }
        if (sp) {
            if (mg == nid - 1) ret = ct, sp = false;
        } else {
            if (mg != nid - 1) sp = true;
        }
    }
    return ret;
}

int main() {
    int cas = 1;
       while (~scanf("%d%d", &n, &m) && (n || m)) {
        while (!pq.empty()) pq.pop();
        memset(vis, 0, sizeof(vis));
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                scanf("%d", &mat[i][j]);
                if (i == 0 || i == n - 1 || j == 0 || j == m - 1) {
                    pq.push(PIII(-mat[i][j], PII(i, j)));
                    vis[i][j] = true;
                }
            }
        }
        //cout << "??" << endl;
        adjust();
        int ans = work();
        if (ans == -1) printf("Case %d: Island never splits.
", cas++);
        else printf("Case %d: Island splits when ocean rises %d feet.
", cas++, ans);
    }    
    return 0;
}

——written by Lyon