main.rs

fn main() {
    let x = Solution::trap(vec![2,0,2]);
    println!("x = {:#?}", x);
}

struct Solution {}

impl Solution {
    pub fn trap(mut height: Vec<i32>) -> i32 {
        while height.len() > 2 && height[0] <= height[1] { height.remove(0); }
        while height.len() > 2 && height[height.len()-1] <= height[height.len()-2] { height.pop(); }
        if height.len() <= 2 { return 0 }
        let mut l = 0;
        let mut r = height.len() - 1;
        let mut lmax = 0;
        let mut rmax = 0;
        let mut water = 0;
        while l <= r {
            if height[l] <= height[r] {
                if height[l] <= lmax {
                    water += lmax - height[l];
                } else {
                    lmax = height[l];
                }
                l += 1;
            } else {
                if height[r] <= rmax {
                    water += rmax - height[r];
                } else {
                    rmax = height[r];
                }
                r -= 1;
            }
        }
        water
    }
}

#[cfg(test)]
mod test {
    use crate::*;

    #[test]
    fn basic() {
        assert_eq!(Solution::trap(vec![0,1,0,2,1,0,1,3,2,1,2,1]), 6);
        assert_eq!(Solution::trap(vec![0,1,2,0,1,3,1,2,0,3,0]), 9);
        assert_eq!(Solution::trap(vec![3,1,2,0,1,3,1,2,0,3,0]), 14);
    }

    #[test]
    fn edge() {
        assert_eq!(Solution::trap(vec![0,1,2,3,2,1,0]), 0);
        assert_eq!(Solution::trap(vec![0,0]), 0);
        assert_eq!(Solution::trap(vec![0,1,2,0]), 0);
    }

    #[test]
    fn leet() {
        assert_eq!(Solution::trap(vec![2,0,2]), 2);
        assert_eq!(Solution::trap(vec![5,4,1,2]), 1);
    }
}