C. Even Picture(思维，构建)

C. Even Picture

题意：给出一个无限大的网格图，要求你在上面涂色，每个涂色方格周围必须有偶数个涂色方格。要求构造出一种涂色方法：只存在n个涂色方格，周围有4个涂色方格（主要是理解题意）。

可以按照图像一直往下延伸。

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 3e5+10;
const int inf = 0x7ffffff;
int f[][2] = {
    
    -1, 0, 0, -1, 0, 1, 1, 0}, n, m;
int s[N];
int read() {
    
    
    int x = 0; int f = 1; char s = getchar();
    while(s < '0' || s > '9') {
    
    if(s == '-') f = -1; s = getchar();}
    while(s >= '0' && s <= '9') {
    
    x = (x << 3) + (x << 1) + s - 48; s = getchar();}
    return x * f;
}
int main() {
    
    
    // freopen("in.txt", "r", stdin);
    // freopen("out.txt", "w", stdout);
    int t;
    t = read();
    cout << 3*t + 4 << endl;
    int a = 1, b = 1;
    //第一个。
    cout << 0 << ' ' << 0 << endl;
    for(int i=0; i<2; i++) {
    
    
        cout << a+f[i][0] << ' ' << b+f[i][1] << endl;
    }
    cout << a << ' ' << b << endl;
    for(int i=2; i<4; i++) {
    
    
        cout << a+f[i][0] << ' ' << b+f[i][1] << endl;
    }
    //后面t-1个。
    for(int i=2; i<=t; i++) {
    
    
        cout << i << ' ' << i << endl;
        for(int j=2; j<4; j++) {
    
    
            cout << i+f[j][0] << ' ' << i + f[j][1] << endl;
        }
    }
    cout << t+1 << ' ' << t+1 << endl;
    return 0;
}