有效子数组的数目

/*
 * Leetcode 1063: Number of Valid Subarrays
 * Given an integer array nums, return the number of non-empty subarrays that are strictly increasing.
 * 
 * Approach using Java Streams:
 * This approach is more functional and uses streams to achieve the same result.
 * 1. We convert the array to a stream of indices.
 * 2. We use a stack to keep track of valid subarrays ending at each index.
 * 3. We use a reduction operation to compute the total count.
 */

import java.util.Stack;
import java.util.stream.IntStream;

public class Solution {
    public int validSubarrays(int[] nums) {
        Stack<Integer> stack = new Stack<>();
        return IntStream.range(0, nums.length).map(i -> {
            while (!stack.isEmpty() && nums[stack.peek()] > nums[i]) {
                stack.pop();
            }
            stack.push(i);
            return stack.size();
        }).sum();
    }
}