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| #include <algorithm>
#include <bitset>
#include <map>
#include <vector>
#include <string>
#include <cstring>
#include <iostream>
#include <cmath>
#include <stack>
#include <set>
#include <queue>
using namespace std;
const double eps = 1e-10;
const double pi = 3.1415926535897932384626433832795;
const double eln = 2.718281828459045235360287471352;
#define f(i, a, b) for (int i = a; i <= b; i++)
#define LL long long
#define IN freopen("in.txt", "r", stdin)
#define OUT freopen("out1.txt", "w", stdout)
#define scan(x) scanf("%d", &x)
#define mp make_pair
#define pb push_back
#define sqr(x) (x) * (x)
#define pr1(x) printf("Case %d: ", x)
#define pn1(x) printf("Case %d:\n", x)
#define pr2(x) printf("Case #%d: ", x)
#define pn2(x) printf("Case #%d:\n", x)
#define lowbit(x) (x & (-x))
#define fi first
#define se second
#define sz(x) int((x).size())
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define summ(a) (accumulate(all(a), 0ll))
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
int n, m, a[51][51], dis[51 * 51], dp[51][51], fa[51 * 51],cor[51*51];
vector<pair<int, int>> v;
pair<int, int> dir[4] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
vector<int> g[51 * 51];
bitset<51 * 51> vis;
int fnd(int x)
{
return fa[x] == x ? x : fa[x] = fnd(fa[x]);
}
int dj(int k)
{
int ans = -1, ck = 0;
if (fnd(k) != k)
return 0x3f3f3f3f;
vis.reset();
memset(dis, 0x3f, sizeof(dis));
dis[k] = 0;
priority_queue<pair<int, int>,vector<pair<int,int>>,greater<pair<int,int>>> q;
q.push({0, k});
while (!q.empty())
{
auto [aa, bb] = q.top();
q.pop();
if (vis[bb])
continue;
vis[bb] = 1;
if(cor[k]&&cor[bb])ans=max(ans,aa+1);
else ans=max(ans,aa);
for (auto it : g[bb])
{
if (aa + 1 < dis[it])
{
dis[it] = aa + 1;
q.push({dis[it], it});
}
}
}
return ans;
}
int main()
{
memset(dis, 0x3f, sizeof(dis));
scanf("%d%d", &n, &m);
for (int i = 1; i <= n; ++i)
{
for (int j = 1; j <= m; ++j)
{
fa[i * m + j - m] = i * m + j - m;
scanf("%d", &a[i][j]);
cor[i * m + j - m]=a[i][j];
}
}
for (int i = 1; i <= n; ++i)
{
for (int j = 1; j <= m; ++j)
{
for (auto [aa, bb] : dir)
{
aa += i, bb += j;
if (aa && bb && aa <= n && bb <= m)
{
int oa = fnd(aa * m + bb - m), ob = fnd(i * m + j - m);
if (a[aa][bb] == a[i][j])
{
fa[ob] = oa;
}
else
v.push_back({oa, ob});
}
}
}
}
for (auto [aa, bb] : v)
{
int oa = fnd(aa), ob = fnd(bb);
g[oa].push_back(ob);
g[ob].push_back(oa);
}
int res = 0x3f3f3f3f;
for (int i = 1; i <= n * m; ++i)
{
res = min(res, dj(i));
}
printf("%d\n", res);
}
|