leetcode简单题26 N.118 杨辉三角 rust描述

//  动态规划
pub fn generate(num_rows: i32) -> Vec<Vec<i32>> {
    let mut triangle: Vec<Vec<i32>> = vec![];

    for i in 0..num_rows {
        let mut row = vec![1; (i + 1) as usize];
        for j in 1..i as usize {
            row[j] = triangle[(i - 1) as usize][(j - 1)] + triangle[(i - 1) as usize][j];
        }
        triangle.push(row);
    }

    triangle
}
use std::collections::HashMap;
// 递归（带缓存）
struct Solution;
impl Solution {
    pub fn generate(num_rows: i32) -> Vec<Vec<i32>> {
        let mut cache = HashMap::new();
        let mut triangle = vec![];

        for i in 0..num_rows {
            let mut row = vec![];
            for j in 0..=i {
                row.push(Self::get_value(i, j, &mut cache));
            }
            triangle.push(row);
        }

        triangle
    }

    fn get_value(i: i32, j: i32, cache: &mut HashMap<(i32, i32), i32>) -> i32 {
        if j == 0 || j == i {
            return 1;
        }

        if let Some(&val) = cache.get(&(i, j)) {
            return val;
        }

        let val = Self::get_value(i - 1, j - 1, cache) + Self::get_value(i - 1, j, cache);
        cache.insert((i, j), val);
        val
    }
}
// 迭代
pub fn generate2(num_rows: i32) -> Vec<Vec<i32>> {
    let mut triangle: Vec<Vec<i32>> = Vec::with_capacity(num_rows as usize);
    for i in 0..num_rows as usize {
        let mut row = vec![1; i + 1];
        for j in 1..i {
            row[j] = triangle[i - 1][j - 1] + triangle[i - 1][j];
        }
        triangle.push(row);
    }
    triangle
}
fn main() {}