README_EN.md

1137. N-th Tribonacci Number

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Description

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.

Solutions

Python3

class Solution:
    def tribonacci(self, n: int) -> int:
        a, b, c = 0, 1, 1
        for _ in range(n):
            a, b, c = b, c, a + b + c
        return a

Java

class Solution {
    public int tribonacci(int n) {
        int a = 0, b = 1, c = 1;
        while (n-- > 0) {
            int d = a + b + c;
            a = b;
            b = c;
            c = d;
        }
        return a;
    }
}

C++

class Solution {
public:
    int tribonacci(int n) {
        long long a = 0, b = 1, c = 1;
        while (n--) {
            long long d = a + b + c;
            a = b;
            b = c;
            c = d;
        }
        return (int) a;
    }
};

Go

func tribonacci(n int) int {
	a, b, c := 0, 1, 1
	for i := 0; i < n; i++ {
		a, b, c = b, c, a+b+c
	}
	return a
}

JavaScript

/**
 * @param {number} n
 * @return {number}
 */
var tribonacci = function(n) {
    let a = 0;
    let b = 1;
    let c = 1;
    while (n--) {
        let d = a + b + c;
        a = b;
        b = c;
        c = d;
    }
    return a;
};

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