Code

#include<iostream>
using namespace std;
#define MAX_SIZE 10005

char map[MAX_SIZE][MAX_SIZE];

int main()
{
	int ans = 0;
	FILE *fp = fopen("2020.txt","r");
	int n=0;
	int m=0;
	if(!fp){
		printf("open file fail!\n");
		exit(1);
	}
	int cur;
	while(!feof(fp)){
		cur = fgetc(fp);
		if(cur=='\n'){
			n++;
			m=0;
			continue;
		}
		map[n][m++]=cur;
	}
	n++;
	for(int i=0;i<n;i++){
		for(int j=0;j<m;j++){
			int nx = i+3;
			int ny = j+3;
			if(map[i][j]!='2') continue;
			
			if(ny<m && 
				map[i][j+1]=='0' &&
				map[i][j+2]=='2' &&
				map[i][j+3]=='0' 
			) // 横向 
				ans++;
			if(nx<n && 
				map[i+1][j]=='0' &&
				map[i+2][j]=='2' &&
				map[i+3][j]=='0' 
			) // 竖向 
				ans++;
			if(nx<n && ny<m &&
				map[i+1][j+1]=='0' &&
				map[i+2][j+2]=='2' &&
				map[i+3][j+3]=='0' 
			) // 斜向 
				ans++;
		}
	}
	cout<<ans;
	return 0;
}

Answer

16520