The problem:

——-

Starting in the top left corner of a 22 grid, there are 6 routes (without backtracking) to the bottom right corner.

How many routes are there through a 2020 grid?

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## My Solution

```
#include <stdio.h>
int main(){
int i,j,x,y;
long long int mat[21][21];
i=0;
for (j=0;j<21;j++)
mat[i][j]=1;
j=0;
for (i=0;i<21;i++)
mat[i][j]=1;
for (i=1;i<21;i++)
for (j=1;j<21;j++)
mat[i][j]=mat[i-1][j]+mat[i][j-1];
for (i=0;i<21;i++){
for (j=0;j<21;j++)
printf("%lld ",mat[i][j]);
printf("n");
}
return 0;
}
```