LeetCode-in-Java

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

public class Solution {
    public int tribonacci(int n) {
        if (n == 0) {
            return 0;
        } else if (n <= 2) {
            return 1;
        } else {
            int tn = 0;
            int tn1 = 1;
            int tn2 = 1;
            int tmp = 0;
            for (int i = 3; i <= n; i++) {
                tmp = tn + tn1 + tn2;
                tn = tn1;
                tn1 = tn2;
                tn2 = tmp;
            }
            return tmp;
        }
    }
}

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