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Problem editorial
The Tribonacci sequence is defined by three initial values: T0 = 0, T1 = 1, and T2 = 1. For every index k >= 3, the next value is the sum of the three preceding values: Tk = T(k - 1) + T(k - 2) + T(k - 3).
N-th Tribonacci Number is a Dynamic Programming (DP) Patterns problem, in the 1D Array (Fibonacci Style) subpattern. The pattern covers fibonacci, Kadane, knapsack, LCS, LIS, edit distance, grid paths, and word break
The reference solution runs in O(n) time and O(1) space.
The full editorial is part of Pro
It explains the core insight, the complexity analysis and the common mistakes, with a worked solution.
N-th Tribonacci Number is a Dynamic Programming (DP) Patterns problem, in the 1D Array (Fibonacci Style) subpattern. Once the approach above makes sense, write it yourself and then work through the neighbouring problems that reuse it.