【hihocoder1291 微软2016校园招聘4月在线笔试D】【逆序思维 并查集】Buiding in Sandbox 我的世界建方块合法性判定

Building in Sandbox

时间限制: 30000ms

单点时限: 3000ms

内存限制: 256MB

描述

Little Hi is playing a sandbox voxel game. In the game the whole world is constructed by massive 1x1x1 cubes. The edges of cubes are parallel to the coordinate axes and the coordinates (x, y, z) of the center of each cube are integers.

At the beginning there is nothing but plane ground in the world. The ground consists of all the cubes of z=0. Little Hi needs to build everything by placing cubes one by one following the rules:

1. The newly placed cube must be adjacent to the ground or a previously placed cube. Two cubes are adjacent if and only if they share a same face.

2. The newly placed cube must be accessible from outside which means by moving in 6 directions(up, down, left, right, forward, backward) there is a path from a very far place - say (1000, 1000, 1000) in this problem - to this cube without passing through ground or other cubes.

Given a sequence of cubes Little Hi wants to know if he can build the world by placing the cubes in such order.

输入

The first line contains the number of test cases T(1 <= T <= 10).

For each test case the first line is N the number of cubes in the sequence.

The following N lines each contain three integers x, y and z indicating the coordinates of a cube.

For 20% of the data, 1 <= N <= 1000, 1 <= x, y, z <= 10.

For 100% of the data, 1 <= N <= 100000, 1 <= x, y, z <= 100.

输出

For each testcase output "Yes" or "No" indicating if Little Hi can place the cubes in such order.

样例提示

In the first test case three cubes are placed on the ground. It's OK.

In the second test case (1, 3, 2) is neither on the ground nor adjacent to previous cubes. So it can't be placed.

In the last test case (2, 2, 1) can not be reached from outside. So it can't be placed.  

样例输入

3
3
1 1 1
1 2 1
1 3 1
3
1 1 1
1 2 1
1 3 2
17
1 1 1
1 2 1
1 3 1
2 3 1
3 3 1
3 2 1
3 1 1
2 1 1
2 1 2
1 1 2
1 2 2
1 3 2
2 3 2
3 3 2
3 2 2
2 2 2
2 2 1

样例输出

Yes
No
No

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<string>
#include<ctype.h>
#include<math.h>
#include<set>
#include<map>
#include<vector>
#include<queue>
#include<bitset>
#include<algorithm>
#include<time.h>
using namespace std;
void fre() { freopen("c://test//input.in", "r", stdin); freopen("c://test//output.out", "w", stdout); }
#define MS(x,y) memset(x,y,sizeof(x))
#define MC(x,y) memcpy(x,y,sizeof(x))
#define MP(x,y) make_pair(x,y)
#define ls o<<1
#define rs o<<1|1
typedef long long LL;
typedef unsigned long long UL;
typedef unsigned int UI;
template <class T1, class T2>inline void gmax(T1 &a, T2 b) { if (b>a)a = b; }
template <class T1, class T2>inline void gmin(T1 &a, T2 b) { if (b<a)a = b; }
const int N = 105, M = 1e5+10, Z = 1e9 + 7, ms63 = 0x3f3f3f3f;
int casenum, casei;
bool e[N][N][N];
int n;
const int dz[6] = { -1,0,0,0,0,1 };
const int dx[6] = { 0,-1,0,0,1,0 };
const int dy[6] = { 0,0,-1,1,0,0 };
struct A
{
	int x, y, z;
}a[M];

const int G = N * N * N;
int f[G];
int find(int x)
{
	return x == f[x] ? x : f[x] = find(f[x]);
}
const int V1 = 102 * 102;
const int V2 = 102;
bool merge(int x1, int y1, int z1, int x2, int y2, int z2)
{
	int o1 = x1*V1 + y1*V2 + z1;
	int o2 = x2*V1 + y2*V2 + z2;
	o1 = find(o1);
	o2 = find(o2);
	if (o1 != o2)
	{
		f[o2] = o1;
		return 1;
	}
	else return 0;
}
bool solve()
{
	MS(e, 0);
	bool flag = 1;
	for (int i = 1; i <= n; ++i)
	{
		scanf("%d%d%d", &a[i].x, &a[i].y, &a[i].z);
		if (!flag)continue;
		int x = a[i].x;
		int y = a[i].y;
		int z = a[i].z;
		if (e[x][y][z])flag = 0;
		e[x][y][z] = 1;
		if (z == 1)continue;
		int k; for (k = 0; k < 6; ++k)
		{
			int xx = x + dx[k];
			int yy = y + dy[k];
			int zz = z + dz[k];
			if (e[xx][yy][zz])break;
		}
		if (k == 6)flag = 0;
	}
	if (!flag)return 0;

	for (int i = 0; i <= 101; ++i)
	{
		for (int j = 0; j <= 101; ++j)
		{
			for (int k = 1; k <= 101; ++k)
			{
				int o = i*V2 + j*V1 + k;
				f[o] = o;
			}
		}
	}

	for (int i = 0; i <= 101; ++i)
	{
		for (int j = 0; j <= 101; ++j)
		{
			for (int k = 1; k <= 101; ++k) if(!e[i][j][k])
			{
				for (int d = 0; d < 6; ++d)
				{
					int x = i + dx[d];
					int y = j + dy[d];
					int z = k + dz[d];
					if (x < 0 || x>101 || y < 0 || y>101 || z < 1 || z>101)continue;
					if (!e[x][y][z])merge(i, j, k, x, y, z);
				}
			}
		}
	}

	for (int i = n; i >= 1; --i)
	{
		int x = a[i].x;
		int y = a[i].y;
		int z = a[i].z;
		e[x][y][z] = 0; 
		for (int d = 0; d < 6; ++d)
		{
			int xx = x + dx[d];
			int yy = y + dy[d];
			int zz = z + dz[d];
			if (xx < 0 || xx>101 || yy < 0 || yy>101 || zz < 1 || zz>101)continue;
			if (!e[xx][yy][zz])merge(x, y, z, xx, yy, zz);
		}
		if (merge(x, y, z, 101, 101, 101))return 0;
	}
	return 1;
}
int main()
{
	scanf("%d", &casenum);
	for (casei = 1; casei <= casenum; ++casei)
	{
		scanf("%d", &n);
		puts(solve() ? "Yes" : "No");
	}
	return 0;
}
/*
【trick&&吐槽】
1，排序的时候千万不要有
if(lastkey!=b.lastkey)return lastkey<b.lastkey
而要直接写成return lastkey<b.lastkey，否则会出错
2，正难则反的"变删除为添加"的思想很常见也很重要
3，这题还要考虑z==0是不可到达的点集（虽然数据中没有这样的）

【题意】
我的世界游戏
建筑可以在地上或者与其它建筑连起来，而且不能完全封闭要与外界极远点相通。
问你一个建筑书序是否合法

【类型】
正难则反 并查集

【分析】
地图很小，可以直接维护100*100*100的所有点
每个方格的放置也就意味着有些点之间的联系被打断。
"联系被打断"不是很好处理，我们正难则反，从最后状态开始向前倒序处理。
一个格子的撤回就变成了关系的连通性。
每个格子都要与极外点（如101*101*101）联通

【时间复杂度&&优化】
O(1e6)

*/