codeforces723 D. Lakes in Berland(并查集)

题目链接：codeforces723 D. Lakes in Berland

参考博客：http://www.cnblogs.com/Geek-xiyang/p/5930245.html

#include<cstdio>
#include<cstring>
#include<vector>
#include<algorithm>
#define CLR(a,b) memset((a),(b),sizeof((a)))
using namespace std;
const int N = 52;
const int M = 2800;
int n, m, k;
char ch[N][N];
int val[N][N];
int fa[M], num[M];
bool vis[M];
int dx[] = {0,0,1,-1};
int dy[] = {1,-1,0,0};
void init(){
    CLR(ch,'.');
    int cnt = 0;
    for(int i = 0; i <= n+1; ++i)
        for(int j = 0; j <= m+1; ++j)
            val[i][j] = ++cnt;
    for(int i = 1; i <= cnt; ++i){
        fa[i] = i;
        num[i] = 1;
    }
}
int fin(int x){
    if(x != fa[x])
        fa[x] = fin(fa[x]);
    return fa[x];
}
void uni(int x, int y){
    if((x = fin(x)) == (y = fin(y))) return;
    else {
        fa[x] = y;
        num[y] += num[x];
    }
}
void make(int i, int j){
    for(int k = 0; k < 4; ++k){
        if(ch[dx[k]+i][dy[k]+j] == '.')
            uni(val[i][j], val[dx[k]+i][dy[k]+j]);
    }
}
bool cmp(int x, int y){
    return num[x] < num[y];
}
vector<int>v;
int main(){
    int i, j, kk, rt, t;
    scanf("%d%d%d", &n, &m, &k);
    init();
    for(i = 0; i <= n+1; ++i){
        uni(val[0][0], val[i][0]);
        uni(val[0][0], val[i][m+1]);
    }
    for(i = 0; i <= m+1; ++i){
        uni(val[0][0], val[0][i]);
        uni(val[0][0], val[n+1][i]);
    }
    for(i = 1; i <= n; ++i){
        scanf("%s", ch[i]+1);
        ch[i][m+1] = '.';//第二遍改时把这句漏了继续WA
    }
    for(i = 1; i <= n; ++i)
        for(j = 1 ; j <= m; ++j)
            if(ch[i][j] == '.')
                make(i, j);
    for(i = 1; i <= n; ++i){
        for(j = 1; j <= m; ++j){
            rt = fin(val[i][j]);
            if(ch[i][j] == '.' && fin(val[0][0]) != rt){
                if(vis[rt]) continue;
                else  vis[rt] = true;
                v.push_back(rt);
            }
        }
    }
    sort(v.begin(), v.end(), cmp);
    int len = v.size();
    t = len;
    int ans = 0;
    if(t > k){
        for(i = 0; i < len; ++i){
            rt = fin(v[i]);
            if(vis[rt]){
                vis[rt] = false;
                t--;
                for(j = 1; j <= n; ++j)
                    for(kk = 1; kk <= m; ++kk)//我第一遍把这里写成k导致WA死
                        if(fin(val[j][kk]) == rt) {ch[j][kk] = '*'; ans++;}
            }
            if(t == k) break;
        }
    }
    printf("%d
", ans);
    for(i = 1; i <= n; ++i){
        for(j = 1; j <= m; ++j)
            printf("%c", ch[i][j]);
        puts("");
    }
    return 0;
}