Submission #111986

#	Time	Username	Problem	Language	Result	Execution time	Memory
111986		qkxwsm	The Kingdom of JOIOI (JOI17_joioi)	C++14	60 / 100	4083 ms	16352 KiB

joioi

//clever
#include <bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define DBG(x) cerr << #x << " = " << (x) << endl
#define SZ(x) ((int) ((x).size()))
#define FOR(i, a, b) for (auto i = (a); i < (b); i++)
#define FORD(i, a, b) for (auto i = (a) - 1; i >= (b); i--)

#define INF 1000000007
#define MAXN 2013

typedef pair<int, int> pii;

int N, M;
int grid[MAXN][MAXN];
int big, small = INF;
pii bigpos, smallpos;
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, -1, 0, 1};
pii range[MAXN];
bitset<MAXN> cb[MAXN], cs[MAXN];

bool valid(int x, int y)
{
	return (0 <= x && x < N && 0 <= y && y < M);
}
bool ok()
{
	//these are the first guys that do not approve!
	FOR(i, 0, N)
	{
		if (range[i].fi >= range[i].se) return false;
	}
	bool flag = true; int pos = 0;
	FOR(i, 0, N)
	{
		//the guy can be in the range (range[i].fi, range[i].se)
		if (range[i].se < pos)
		{
			flag = false; break;
		}
		pos = max(pos, range[i].fi + 1);
	}
	if (flag) return true;
	flag = true; pos = M - 1;
	FOR(i, 0, N)
	{
		if (range[i].fi > pos)
		{
			flag = false; break;
		}
		pos = min(pos, range[i].se - 1);
	}
	if (flag) return true;
	return false;
}

bool check(int c)
{
	//try to merge stuff with small!
	FOR(i, 0, N)
	{
		cb[i].reset();
		cs[i].reset();
	}
	queue<pii> q;
	q.push(bigpos);
	cb[bigpos.fi][bigpos.se] = 1;
	while(!q.empty())
	{
		int x = q.front().fi, y = q.front().se;
		q.pop();
		FOR(d, 0, 4)
		{
			pii p = {x + dx[d], y + dy[d]};
			if (valid(p.fi, p.se) && (grid[p.fi][p.se] >= big - c) && !(cb[p.fi][p.se]))
			{
				q.push(p);
				cb[p.fi][p.se] = 1;
			}
		}
	}
	q.push(smallpos);
	cs[smallpos.fi][smallpos.se] = 1;
	while(!q.empty())
	{
		int x = q.front().fi, y = q.front().se;
		q.pop();
		FOR(d, 0, 4)
		{
			pii p = {x + dx[d], y + dy[d]};
			if (valid(p.fi, p.se) && (grid[p.fi][p.se] <= small + c) && !cs[p.fi][p.se])
			{
				q.push(p);
				cs[p.fi][p.se] = 1;
			}
		}
	}
	//try to have SMALL be an increasing/decreasing sequence!
	FOR(i, 0, N)
	{
		for (range[i].se = 0; range[i].se < M; range[i].se++)
		{
			if (!cs[i][range[i].se]) break;
		}
		for (range[i].fi = M - 1; range[i].fi >= 0; range[i].fi--)
		{
			if (!cb[i][range[i].fi]) break;
		}
	}
	if (ok())
	{
		return true;
	}
	//try to have BIG be an increasing/decreasing sequence
	FOR(i, 0, N)
	{
		for (range[i].se = 0; range[i].se < M; range[i].se++)
		{
			if (!cb[i][range[i].se]) break;
		}
		for (range[i].fi = M - 1; range[i].fi >= 0; range[i].fi--)
		{
			if (!cs[i][range[i].fi]) break;
		}
	}
	if (ok())
	{
		return true;
	}
	return false;
}

int32_t main()
{
	ios_base::sync_with_stdio(0); cin.tie(0);
	// cout << fixed << setprecision(10);
	// cerr << fixed << setprecision(10);
	// if (fopen("file.in", "r"))
	// {
	// 	freopen ("file.in", "r", stdin);
	// 	freopen ("file.out", "w", stdout);
	// }
	cin >> N >> M;
	FOR(i, 0, N)
	{
		FOR(j, 0, M)
		{
			cin >> grid[i][j];
			if (grid[i][j] > big)
			{
				big = grid[i][j];
				bigpos = {i, j};
			}
			if (grid[i][j] < small)
			{
				small = grid[i][j];
				smallpos = {i, j};
			}
		}
	}
	// cerr << smallpos.fi << ' ' << smallpos.se << ' ' << bigpos.fi << ' ' << bigpos.se << endl;
	int lo = 0, hi = big - small;
	while(hi > lo)
	{
		int mid = (hi + lo) >> 1;
		if (check(mid)) hi = mid;
		else lo = mid + 1;
	}
	cout << lo << '\n';
	// cerr << "time elapsed = " << (clock() / (CLOCKS_PER_SEC / 1000)) << " ms" << endl;
	return 0;
}
/* READ READ READ
* int overflow, maxn too small, special cases (n=1?, two distinct?), cin.tie() interactive
* reread the problem, try small cases
* note down possible sources of error as you go
* do smth instead of nothing
*/

• Subtask 1: 15 / 15
• Subtask 2: 45 / 45
• Subtask 3: 0 / 40