LeetCode in Kotlin

1137. N-th Tribonacci Number

Easy

The Tribonacci sequence T_n is defined as follows:

T₀ = 0, T₁ = 1, T₂ = 1, and T_n+3 = T_n + T_n+1 + T_n+2 for n >= 0.

Given n, return the value of T_n.

Example 1:

Input: n = 4

Output: 4

Explanation: T_3 = 0 + 1 + 1 = 2 T_4 = 1 + 1 + 2 = 4

Example 2:

Input: n = 25

Output: 1389537

Constraints:

• 0 <= n <= 37
• The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.

Solution

class Solution {
    fun tribonacci(n: Int): Int = if (n == 0) {
        0
    } else if (n <= 2) {
        1
    } else {
        var tn = 0
        var tn1 = 1
        var tn2 = 1
        var tmp = 0
        for (i in 3..n) {
            tmp = tn + tn1 + tn2
            tn = tn1
            tn1 = tn2
            tn2 = tmp
        }
        tmp
    }
}

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