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//! 最大長方形

use std::collections::VecDeque;

pub fn largest_rectangle(arg: &[i64]) -> i64 {
    let mut histogram = arg.to_vec();
    histogram.push(0);

    let mut stack = VecDeque::new();
    let mut ans = 0;

    for (right, &h) in histogram.iter().enumerate() {
        if let Some(&(_, value)) = stack.back() {
            if value <= h {
                stack.push_back((right as i64, h));
                continue;
            }
        }
        let mut most_left = right as i64;
        while !stack.is_empty() && stack[stack.len() - 1].1 > h {
            let (left, value) = stack.pop_back().unwrap();
            most_left = left;
            ans = ans.max(value * (right as i64 - most_left));
        }
        stack.push_back((most_left, h));
    }

    ans
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_largest_rectangle() {
        assert_eq!(largest_rectangle(&[0, 2, 5, 6, 4, 2, 3, 1]), 12);
        assert_eq!(largest_rectangle(&[2, 4, 4, 9, 4, 9]), 20);
        assert_eq!(largest_rectangle(&[200, 4, 4, 9, 4, 9]), 200);
    }
}