Codeforces Round #614 (Div. 2) C. NEKO's Maze Game

原题：
NEKO#ΦωΦ has just got a new maze game on her PC!

The game’s main puzzle is a maze, in the forms of a 2×n2×n rectangle grid. NEKO’s task is to lead a Nekomimi girl from cell (1,1)(1,1) to the gate at (2,n)(2,n) and escape the maze. The girl can only move between cells sharing a common side.

However, at some moments during the game, some cells may change their state: either from normal ground to lava (which forbids movement into that cell), or vice versa (which makes that cell passable again). Initially all cells are of the ground type.

After hours of streaming, NEKO finally figured out there are only qq such moments: the ii-th moment toggles the state of cell (ri,ci)(ri,ci) (either from ground to lava or vice versa).

Knowing this, NEKO wonders, after each of the qq moments, whether it is still possible to move from cell (1,1)(1,1) to cell (2,n)(2,n) without going through any lava cells.

Although NEKO is a great streamer and gamer, she still can’t get through quizzes and problems requiring large amount of Brain Power. Can you help her?

Input
The first line contains integers nn, qq (2≤n≤1052≤n≤105, 1≤q≤1051≤q≤105).

The ii-th of qq following lines contains two integers riri, cici (1≤ri≤21≤ri≤2, 1≤ci≤n1≤ci≤n), denoting the coordinates of the cell to be flipped at the ii-th moment.

It is guaranteed that cells (1,1)(1,1) and (2,n)(2,n) never appear in the query list.

Output
For each moment, if it is possible to travel from cell (1,1)(1,1) to cell (2,n)(2,n), print “Yes”, otherwise print “No”. There should be exactly qq answers, one after every update.

You can print the words in any case (either lowercase, uppercase or mixed).

Example
inputCopy
5 5
2 3
1 4
2 4
2 3
1 4
outputCopy
Yes
No
No
No
Yes
Note
We’ll crack down the example test here:

After the first query, the girl still able to reach the goal. One of the shortest path ways should be: (1,1)→(1,2)→(1,3)→(1,4)→(1,5)→(2,5)(1,1)→(1,2)→(1,3)→(1,4)→(1,5)→(2,5).
After the second query, it’s impossible to move to the goal, since the farthest cell she could reach is (1,3)(1,3).
After the fourth query, the (2,3)(2,3) is not blocked, but now all the 44-th column is blocked, so she still can’t reach the goal.
After the fifth query, the column barrier has been lifted, thus she can go to the final goal again.
题意：2*n格子，从（1,1）走到（2，n）,有q次操作，每次可以把一个格子从开变成关，或者从关变成开，判断可不可以走通。
思路：画一下图很明显发现，如果关第一层的某格子（位置1，y），只要同时第二层的(2,y),(2,y-1),(2,y+1)中有一个也关的，就走不通！关第二层也一样，至于开，就操作反一下即可。然后统计这对应三点关闭的个数，用cnt存一下，只要cnt不为0，一定不能过去，直到某次操作后cnt为0就能过!
题目链接

#include
#include
#include
#include
#include
#include
#include
#include
#include 
#include
#include
#include
#include 
#include
using namespace std;
int m1[10][200010];
int main()
{
    int n,z,sum=0;
    int x,y;
    cin>>n>>z;
    for(int i=1;i<= z;i++)
    {
        cin>>x>>y;
        if(m1[x][y])
            sum-=m1[3-x][y - 1] + m1[3-x][y] + m1[3-x][y + 1];//3-x是指一层时考虑2层，2层时考虑一层 
        else
            sum+=m1[3-x][y - 1] + m1[3-x][y] + m1[3-x][y + 1];
        if(!sum) printf("Yes\n");//sum是现在的堵塞情况 
        else
        	printf("No\n");
        m1[x][y] ^= 1;//进行开关状态值改变 
    }
}