N-th Tribonacci Number Problem & Solution
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.
See the n-th tribonacci number problem on LeetCode.
C++ Solution
#pragma GCC optimize("Ofast")
#pragma GCC optimization("fast-math")
#pragma GCC optimization("unroll-loops")
#pragma GCC target("avx,avx2,fma")
static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();
class Solution {
public:
int tribonacci(int n) {
int t0 = 0;
int t1 = 1;
int t2 = 1;
if (n == 0) { return t0; }
if (n == 1) { return t1; }
if (n == 2) { return t2; }
for (int i = 3; i <= n; ++i) {
int t3 = t2 + t1 + t0;
t0 = t1;
t1 = t2;
t2 = t3;
}
return t2;
}
};