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NthTribonacciNumber.java
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NthTribonacciNumber.java
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package algorithms;
import org.junit.Test;
import static org.junit.Assert.assertEquals;
/**
* 1137. N-th Tribonacci Number
* https://leetcode.com/problems/n-th-tribonacci-number/
* Difficulty : Easy
* Related Topics : Math, Dynamic Programming, Memoization
*
* 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.
*
* created by Cenk Canarslan on 2021-11-21
*/
public class NthTribonacciNumber {
@Test
public void testNthTribonacciNumber() {
assertEquals(4, tribonacci(4));
assertEquals(1389537, tribonacci(25));
}
/**
* Runtime: 0 ms, faster than 100.00% of Java online submissions for N-th Tribonacci Number.
* Memory Usage: 35.8 MB, less than 37.42% of Java online submissions for N-th Tribonacci Number.
*
* @param n
* @return
*/
public int tribonacci(int n) {
int[] memo = new int[n+1];
if (n == 0 || n==1) return n;
memo[0] = 0;
memo[1] = 1;
memo[2] = 1;
for (int i = 3; i <= n; i++) {
memo[i] = memo[i-3] + memo[i-2] + memo[i-1];
}
return memo[n];
}
}