Introduction

In this blog post, we will explore how to solve the LeetCode problem "2110" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

You are given an integer array prices representing the daily price history of a stock, where prices[i] is the stock price on the ith day. A smooth descent period of a stock consists of one or more contiguous days such that the price on each day is lower than the price on the preceding day by exactly 1. The first day of the period is exempted from this rule. Return the number of smooth descent periods. Example 1: Input: prices = [3,2,1,4] Output: 7 Explanation: There are 7 smooth descent periods: [3], [2], [1], [4], [3,2], [2,1], and [3,2,1] Note that a period with one day is a smooth descent period by the definition. Example 2: Input: prices = [8,6,7,7] Output: 4 Explanation: There are 4 smooth descent periods: [8], [6], [7], and [7] Note that [8,6] is not a smooth descent period as 8 - 6 ≠ 1. Example 3: Input: prices = [1] Output: 1 Explanation: There is 1 smooth descent period: [1] Constraints: 1 <= prices.length <= 105 1 <= prices[i] <= 105

Explanation

Here's an efficient solution to the problem, along with an explanation:

• High-Level Approach:

  • Iterate through the prices array.
  • Maintain a length variable representing the current smooth descent period's length.
  • If the current price follows the smooth descent pattern (price is exactly 1 less than the previous), increment length. Otherwise, reset length to 1 (a single-day descent).
  • Accumulate the length into the total count. This works because each smooth descent of length n contributes n sub-periods.

• Complexity:

  • Runtime Complexity: O(n) - We iterate through the array once.
  • Storage Complexity: O(1) - We use only a few constant extra variables.

Code

    def count_smooth_descent_periods(prices):
    """
    Counts the number of smooth descent periods in an array of stock prices.

    Args:
        prices: A list of integers representing the daily stock prices.

    Returns:
        The number of smooth descent periods.
    """

    n = len(prices)
    total = 0
    length = 1

    for i in range(n):
        if i > 0 and prices[i] == prices[i - 1] - 1:
            length += 1
        else:
            length = 1
        total += length

    return total