[LeetCode] 1137. N-th Tribonacci Number

 轉自LeetCode

The Tribonacci sequence Tn is defined as follows: 

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

Given n, return the value of Tn.

 

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

509. Fibonacci Number 的衍生題

不難，就是照著題意做

kotlin

	class Solution {
	fun tribonacci(n: Int): Int {
	return when {
	n == 0 -> 0
	n == 1 -> 1
	n == 2 -> 1
	else -> {
	var first = 0
	var second = 1
	var third = 1
	var target = n - 2
	var tmp = 0
	while(target > 0) {
	tmp = first
	first = second
	second = third
	third = tmp + first + second
	--target
	}
	third
	}
	}
	}
	}

view raw n-th_tribonacci_number.kt hosted with ❤ by GitHub