Solution.rs

use std::collections::VecDeque;

impl Solution {
    pub fn sum_subarray_mins(arr: Vec<i32>) -> i32 {
        let n = arr.len();
        let mut left = vec![-1; n];
        let mut right = vec![n as i32; n];
        let mut stk: VecDeque<usize> = VecDeque::new();

        for i in 0..n {
            while !stk.is_empty() && arr[*stk.back().unwrap()] >= arr[i] {
                stk.pop_back();
            }
            if let Some(&top) = stk.back() {
                left[i] = top as i32;
            }
            stk.push_back(i);
        }

        stk.clear();
        for i in (0..n).rev() {
            while !stk.is_empty() && arr[*stk.back().unwrap()] > arr[i] {
                stk.pop_back();
            }
            if let Some(&top) = stk.back() {
                right[i] = top as i32;
            }
            stk.push_back(i);
        }

        let MOD = 1_000_000_007;
        let mut ans: i64 = 0;
        for i in 0..n {
            ans +=
                ((((right[i] - (i as i32)) * ((i as i32) - left[i])) as i64) * (arr[i] as i64)) %
                MOD;
            ans %= MOD;
        }
        ans as i32
    }
}