795. Number of Subarrays with Bounded Maximum

We are given an array A of positive integers, and two positive integers L and R (L <= R).

Return the number of (contiguous, non-empty) subarrays such that the value of the maximum array element in that subarray is at least L and at most R.

Example :
Input: 
A = [2, 1, 4, 3]
L = 2
R = 3
Output: 3
Explanation: There are three subarrays that meet the requirements: [2], [2, 1], [3].

Note:

  • L, R  and A[i] will be an integer in the range [0, 10^9].
  • The length of A will be in the range of [1, 50000].

Rust Solution

struct Solution;

impl Solution {
    fn num_subarray_bounded_max(a: Vec<i32>, l: i32, r: i32) -> i32 {
        let n = a.len();
        let mut start = 0;
        let mut end = 0;
        let mut res = 0;
        for i in 0..n {
            if a[i] > r {
                start = i + 1;
            }
            if a[i] >= l {
                end = i + 1;
            }
            if start < end {
                res += end - start;
            }
        }
        res as i32
    }
}

#[test]
fn test() {
    let a = vec![2, 1, 4, 3];
    let l = 2;
    let r = 3;
    let res = 3;
    assert_eq!(Solution::num_subarray_bounded_max(a, l, r), res);
}

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