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1137-n-th-tribonacci-number.js
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// 1137. N-th Tribonacci Number
// https://leetcode.com/problems/n-th-tribonacci-number/
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// Runtime: 52 ms, faster than 63.26% of JavaScript online submissions
// Memory Usage: 34 MB, less than 100.00% of JavaScript online submissions
/**
* @param {number} n
* @return {number}
*/
// const tribonacci = n => {
// let [x, y, z] = [0, 1, 1];
// if (n < 3) return [x, y, z][n];
// for (i = 3; i < n; i++) [x, y, z] = [y, z, x + y + z];
// return x + y + z;
// };
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// Runtime: 100 ms, faster than 8.21% of JavaScript online submissions
// Memory Usage: 33.5 MB, less than 100.00% of JavaScript online submissions
// const tribonacci = n => {
// const a = [0, 1, 1];
// for (let i = 3; i <= n; i++) a[i] = a[i - 3] + a[i - 2] + a[i - 1];
// return a[n];
// };
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// Runtime: 56 ms, faster than 50.36% of JavaScript online submissions
// Memory Usage: 33.8 MB, less than 100.00% of JavaScript online submissions
const tribonacci = n =>
[
0,
1,
1,
2,
4,
7,
13,
24,
44,
81,
149,
274,
504,
927,
1705,
3136,
5768,
10609,
19513,
35890,
66012,
121415,
223317,
410744,
755476,
1389537,
2555757,
4700770,
8646064,
15902591,
29249425,
53798080,
98950096,
181997601,
334745777,
615693474,
1132436852,
2082876103,
][n];
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
import { strictEqual } from 'assert';
strictEqual(tribonacci(0), 0);
strictEqual(tribonacci(1), 1);
strictEqual(tribonacci(2), 1);
strictEqual(tribonacci(3), 2);
strictEqual(tribonacci(4), 4);
strictEqual(tribonacci(5), 7);
strictEqual(tribonacci(6), 13);
strictEqual(tribonacci(25), 1389537);
// =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
/*
t0 = 0 + 1 + 1 = 0
t1 = 0 + 1 + 1 = 1
t2 = 0 + 1 + 1 = 1
t3 = 0 + 1 + 1 = 2
t4 = 1 + 1 + 2 = 4
t5 = 1 + 2 + 4 = 7
t6 = 2 + 4 + 7 = 13
*/