struct Solution;
impl Solution {
    pub fn generate(num_rows: i32) -> Vec<Vec<i32>> {
        let mut ans : Vec<Vec<i32>>= vec![vec![1]];
        for i in 1..num_rows {
            let mut row = vec![1];
            let prev_row = &ans[(i - 1) as usize];
            for j in 1..prev_row.len() {
                row.push(prev_row[j - 1] + prev_row[j]);
            }
            row.push(1);
            ans.push(row);
        }
        ans
    }
}

fn main() {
    let sl = Solution::generate(7);
    println!("{:?}", sl);
}