(联通快缩点加bfs)F - Paint the Grid Reloaded

最新推荐文章于 2025-09-06 09:45:09 发布

原创最新推荐文章于 2025-09-06 09:45:09 发布 · 195 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#图论

本文通过一个具体的编程竞赛题目，深入解析了图论的基本概念及其应用，展示了深度优先搜索(DFS)与广度优先搜索(BFS)算法在解决图论问题中的实际运用。通过对代码的详细解读，读者可以了解到如何构建图数据结构，如何利用DFS进行图的遍历，以及如何使用BFS寻找最短路径。此外，还介绍了图的连通性和图着色等概念。

https://vjudge.net/contest/294469#problem/F

#pragma comment (linker,"/STACK:1024000000,1024000000")
#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#include<cstdlib>
#include<cmath>
#include<stack>
#include<map>
#include<vector>
#include<algorithm>
using namespace std;
#define ll long long
#define lb long double
#define INF 0x3f3f3f3f
const int maxn = 45;
const ll mod = 1e9 + 7;
int t, n, m, cnt, num, mini = INF;
char s[maxn][maxn];
int head[maxn*maxn], col[maxn][maxn];
bool judge[maxn*maxn][maxn*maxn], vis[maxn*maxn];
int dir[4][2] = {1, 0, 0, -1, -1, 0, 0, 1};
struct node{
	int to;
	int next;
}edge[maxn*maxn*maxn*maxn];
struct nod{
	int u;
	int d;
};
void add(int u, int v){
	edge[cnt].to = v;
	edge[cnt].next = head[u];
	head[u] = cnt ++;
}
void init(){
	scanf("%d %d", &n, &m);
	getchar();
	for(int i = 1 ; i <= n ; ++ i){
		scanf("%s", s[i] + 1);
	}
	cnt = 0;
	num = 0;
	mini = INF;
	//memset(edge, 0, sizeof(edge));
	memset(judge, 0, sizeof(judge));
	memset(col, -1, sizeof(col));
	memset(head, -1, sizeof(head));
}
void dfs(int x, int y, int c){
	for(int i = 0 ; i < 4 ; ++ i){
		int tx = x + dir[i][0];
		int ty = y + dir[i][1];
		if(tx < 1 || tx > n || ty < 1 || ty > m) continue;
		if(s[x][y] == s[tx][ty]){
			if(col[tx][ty] == -1){
				col[tx][ty] = c;
				dfs(tx, ty, c);
			}
		}
		else{
			if(col[tx][ty] != -1){
				int u = col[x][y], v = col[tx][ty];
				if(!judge[u][v] && u != v){
					add(u, v); add(v, u);
					judge[u][v] = 1; judge[v][u] = 1;
				}
			}
		}
	}
}
int bfs(int s){
	int maxi = 0;
	memset(vis, 0, sizeof(vis));
	queue<nod> que;
	vis[s] = 1;
	nod temp;
	temp.u = s; temp.d = 0;
	que.push(temp);
	while(!que.empty()){
		nod cur = que.front();
		que.pop();
		if(cur.d > mini) return INF;
		for(int i = head[cur.u] ; i != -1 ; i = edge[i].next){
			int tt = edge[i].to;
			if(tt == cur.u) continue;
			if(!vis[tt]){
				vis[tt] = 1;
				nod temp;
				temp.u = tt; temp.d = cur.d + 1;
				que.push(temp);
				maxi = max(maxi, cur.d + 1);
			}
		}
	}
	return maxi;
}
int main()
{
	scanf("%d", &t);
	while(t--){
		init();
		for(int i = 1 ; i <= n ; ++ i){
			for(int j = 1 ; j <= m ; ++ j){
				if(col[i][j] == -1){
					col[i][j] = ++ num;
					dfs(i, j, num);
				}
			}
		}
		for(int i = 1 ; i <= num ; ++ i){
			mini = min(mini, bfs(i));
		}
		printf("%d\n", mini);
	}
    return 0;
}