Project Euler Problem 15

问题：

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?

答案：137846528820

类似于杨辉三角的解决方法：

#include

int main(void)
{
    long long grid[21][21] = {{0L}};

    int i=0,j=0;

    for(i=0; i<21; i++)
        grid[0][i]=grid[i][0]=1;

    for(i=1; i<21; i++)
        for(j=1; j<21; j++)
                grid[i][j] = grid[i-1][j] + grid[i][j-1];

    printf("The numbers of way is %lli\n", grid[20][20]);
    return 0;
}