[LeetCode/Easy] 1137. N-th Tribonacci Number

1. Input

1) 정수 n

 

2. Output

1) n번째 트리보나치 수

2) T_0 = 0, T_1 = 1, T_2 = 1, T_n+3 = T_n + T_n+1 + T_n+2 (n>=0)

 

3. Constraint

1) 0 <= n <= 37

2) 0<= answer <= 2^31 - 1

 

4. Example

Input: n = 4 -> Output: 4

설명:

T_3 = 0 + 1 + 1 = 2

T_4 = 1 + 1 + 2 = 4

 

5. Code

1) 첫 코드(2022/07/06)

if(n==0)
    return 0;

if(n==1 || n==2)
    return 1;

int a=0, b=1, c=1, d=0;

for(int i=3 ; i<=n ; i++){
    d = a+b+c;
    a = b;
    b = c;
    c = d;
}

return d;