Overview

This problem requires looking at the temperature differences between adjacent checkpoints in order and counting the number of times \(|T_i - T_{i-1}| \ge K\) is satisfied.
It can be solved by simply comparing each consecutive pair from the beginning.

Analysis

The key point is that the determination of a sudden change depends only on “two adjacent points.”
In other words, to evaluate checkpoint \(i\), only \(T_i\) and \(T_{i-1}\) are needed — no earlier information is required.

For example, when
\(N=5,\ K=4,\ T=[10, 13, 8, 15, 14]\):

• \(|13-10|=3\) (not a sudden change)
• \(|8-13|=5\) (sudden change)
• \(|15-8|=7\) (sudden change)
• \(|14-15|=1\) (not a sudden change)

So the answer is \(2\).

Even with a straightforward approach, nothing beyond “checking all adjacent pairs” is necessary.
This method requires \(N-1\) comparisons, which is sufficiently fast even for the constraint \(N \le 10^5\).

Also, you don’t need to store the entire temperature array — you can make the determination by keeping only the previous temperature prev.
This reduces memory usage.

Algorithm

1. Read \(N, K\).
2. Store the first temperature \(T_1\) in prev.
3. Repeat for \(i=2\) to \(N\):
   • Read the current temperature as cur.
   • If \(|cur - prev| \ge K\), increment the count by 1.
   • Update prev = cur.
4. Output the count.

This flow matches the provided code.

Complexity

• Time complexity: \(O(N)\)
• Space complexity: \(O(1)\) (when not storing the input array)

Implementation Notes

• The loop runs from checkpoint \(2\) to \(N\), so use for _ in range(2, N + 1):.

• The condition uses “greater than or equal to,” so use >= K (not >).

• In Python, abs(cur - prev) safely computes the absolute value.

• Since the input can be relatively large, using sys.stdin.readline ensures stable and fast reading.

  Source Code

import sys

def main():
    input = sys.stdin.readline
    N, K = map(int, input().split())
    prev = int(input().strip())
    count = 0

    for _ in range(2, N + 1):
        cur = int(input().strip())
        if abs(cur - prev) >= K:
            count += 1
        prev = cur

    print(count)

if __name__ == "__main__":
    main()

This editorial was generated by gpt-5.3-codex.