ZOJ 3781 Paint the Grid Reloaded BFS

来源：互联网发布：网络彩票销售好做吗编辑：程序博客网时间：2024/06/05 04:27

题意：

给定n*m 的矩阵

每个格子有O X 两种颜色

可以选择1个同颜色的块，翻转为另一个颜色。

问翻转为只有1种颜色需要最小几次操作

bfs枚举每个第一次选择的节点

#include<stdio.h>#include<iostream>#include<algorithm>#include<string.h>#include<math.h>#include<vector>#include<queue>#include<set>using namespace std;#define N 45#define inf 100000000int n,m;char mp[N][N];int Hash(int x, int y){return x*m+y;}int f[N*N],F[N][N];int find(int x){return x==f[x]?x:f[x]=find(f[x]);}void Union(int x,int y){int fx = find(x), fy = find(y);if(fx<fy)swap(fx,fy);f[fx] = fy;}vector<int>G[N*N];void ADD(){for(int i = 0; i < n; i++)for(int j = 0; j < m; j++){if(i-1>=0 && F[i-1][j] != F[i][j])G[F[i-1][j]].push_back(F[i][j]), G[F[i][j]].push_back(F[i-1][j]);if(j-1>=0 && F[i][j-1] != F[i][j])G[F[i][j-1]].push_back(F[i][j]), G[F[i][j]].push_back(F[i][j-1]);}for(int i = 0; i < n*n; i++){sort(G[i].begin(), G[i].end());G[i].resize(unique(G[i].begin(), G[i].end())-G[i].begin());}}int vis[N*N];int bfs(int u){int ans = 0;memset(vis, -1, sizeof vis);queue<int>q; q.push(u); vis[u] = 0;while(!q.empty()){int u = q.front(); q.pop();ans = max(ans, vis[u]);for(int i = 0; i < G[u].size(); i++){int v = G[u][i]; if(vis[v]!=-1)continue;vis[v] = vis[u]+1;q.push(v);}}return ans;}set<int>myset;void init(){myset.clear();for(int i = 0; i <= n*m; i++)f[i] = i ,G[i].clear();}int main(){int T;scanf("%d",&T);int i, j;while(T--){scanf("%d %d",&n,&m);init();for(i = 0; i < n; i++)scanf("%s",mp[i]);for(i = 0; i < n; i++){for(j = 0; j < m; j++){int now = Hash(i,j);int a = Hash(i,j-1), b = Hash(i-1,j);if(i-1>=0 && mp[i-1][j] == mp[i][j])Union(now,b);if(j-1>=0 && mp[i][j-1] == mp[i][j])Union(now,a);}}for(i = 0; i < n*m; i++)find(i);for(i = 0; i < n*m; i++)myset.insert(f[i]);//for(set<int>::iterator p=myset.begin(); p != myset.end(); p++)G[n*n].push_back(*p);for(i = 0; i < n; i++)for(j = 0; j < m; j++)F[i][j] = f[Hash(i,j)];ADD();int A = inf;for(set<int>::iterator p=myset.begin(); p != myset.end(); p++)A = min(A, bfs(*p));printf("%d\n",A);}return 0;}

0 0