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LeetCode practice July 15th 2026

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239 views8likes3:11:26midnight_simonOriginal Release: 2026-07-16

Digit DP is a dynamic programming technique used to count numbers satisfying specific digit-based constraints within a given range. The technique involves breaking down the problem by digit position, tracking constraints like previous digits, and using memoization to avoid redundant calculations. For the problem of counting numbers where the absolute difference between adjacent digits is at most K, the solution requires tracking the previous digit and the tight constraint (whether we're still bounded by the upper limit of the range). The approach handles leading zeros carefully and computes the count for the upper bound minus the count for the lower bound minus one to get the result for the range.