2999. Count the Number of Powerful Integers | Leetcode Daily - Python
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Dive deep into LeetCode 2999, "Count the Number of Powerful Integers," in this detailed explanation. We break down the problem of finding integers within a given range (`start` to `finish`) that satisfy two conditions: ending with a specific suffix `s` and having all digits less than or equal to a `limit`. Learn why a simple brute-force check is too slow for large ranges and discover the common range counting technique: calculating `count(= finish) - count(= start - 1)`. The core of the solution lies in Digit Dynamic Programming (Digit DP). Follow along as we build the DP solution step-by-step, defining the state (`index`, `tight` constraint, `is_leading` zero), and carefully incorporating the digit limit and suffix matching rules within the recursive `dfs` function. We'll walk through the Python code implementation, explaining the main logic, the `calculate` helper, and the crucial `dfs` transitions, along with analyzing the time and space complexity.
Perfect for coding interview preparation and improving problem-solving skills.
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Solution Link: https://leetcode.com/problems/count-t...
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