1137. N-th Tribonacci Number

Posted 2020-11-27 johnnyzhao

package LeetCode_1137

/**
 * 1137. N-th Tribonacci Number
 * https://leetcode.com/problems/n-th-tribonacci-number/description/
 *
 * 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
 * */
class Solution {
    fun tribonacci(n: Int): Int {
        if (n<=1){
            return n
        }
        if (n==2){
            return 1
        }
        val dp = IntArray(n+1)
        dp[0] = 0
        dp[1] = 1
        dp[2] = 1
        for (i in 3 .. n){
            dp[i] = dp[i-3]+dp[i-2]+dp[i-1]
        }
        return dp[dp.size-1]
    }
}