1063. Number of Valid Subarrays

Given an array A of integers, return the number of non-empty continuous subarrays that satisfy the following condition:

The leftmost element of the subarray is not larger than other elements in the subarray.

 

Example 1:

Input: [1,4,2,5,3]
Output: 11
Explanation: There are 11 valid subarrays: [1],[4],[2],[5],[3],[1,4],[2,5],[1,4,2],[2,5,3],[1,4,2,5],[1,4,2,5,3].

Example 2:

Input: [3,2,1]
Output: 3
Explanation: The 3 valid subarrays are: [3],[2],[1].

Example 3:

Input: [2,2,2]
Output: 6
Explanation: There are 6 valid subarrays: [2],[2],[2],[2,2],[2,2],[2,2,2].

 

Note:

  1. 1 <= A.length <= 50000
  2. 0 <= A[i] <= 100000

Rust Solution

struct Solution;

impl Solution {
    fn valid_subarrays(nums: Vec<i32>) -> i32 {
        let mut stack = vec![];
        let mut res = 0;
        for x in nums {
            while let Some(&top) = stack.last() {
                if top > x {
                    stack.pop();
                } else {
                    break;
                }
            }
            stack.push(x);
            res += stack.len();
        }
        res as i32
    }
}

#[test]
fn test() {
    let nums = vec![1, 4, 2, 5, 3];
    let res = 11;
    assert_eq!(Solution::valid_subarrays(nums), res);
    let nums = vec![3, 2, 1];
    let res = 3;
    assert_eq!(Solution::valid_subarrays(nums), res);
    let nums = vec![2, 2, 2];
    let res = 6;
    assert_eq!(Solution::valid_subarrays(nums), res);
}

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