Solution.rs

use std::collections::VecDeque;

impl Solution {
    pub fn can_finish(mut num_courses: i32, prerequisites: Vec<Vec<i32>>) -> bool {
        let mut g: Vec<Vec<i32>> = vec![vec![]; num_courses as usize];
        let mut indeg: Vec<i32> = vec![0; num_courses as usize];

        for p in prerequisites {
            let a = p[0] as usize;
            let b = p[1] as usize;
            g[b].push(a as i32);
            indeg[a] += 1;
        }

        let mut q: VecDeque<usize> = VecDeque::new();
        for i in 0..num_courses {
            if indeg[i as usize] == 0 {
                q.push_back(i as usize);
            }
        }

        while let Some(i) = q.pop_front() {
            num_courses -= 1;
            for &j in &g[i] {
                let j = j as usize;
                indeg[j] -= 1;
                if indeg[j] == 0 {
                    q.push_back(j);
                }
            }
        }

        num_courses == 0
    }
}