Dynamic planning daily practice (1)

1. Fibonacci

class Solution {
    
public:
    int fib(int n) {
    
        if(n<=1)
        {
    
            return n;
        }
        else{
    
            int q=0,p=0,s=1;
            for(int i=2;i<=n;++i)
            {
    
                q=p;
                p=s;
                s=p+q;
            }
             return s;
        }
       
    }
};

The boundary condition of Fibonacci number is F(0)=0F(0)=0 and F(1)=1F(1)=1. When n>1n>1 when , The sum of each term is equal to the sum of the first two terms , Therefore, there is the following recurrence relationship ：

F(n)=F(n-1)+F(n-2)
F(n)=F(n−1)+F(n−2)

2.T Teponacci sequence

T0 = 0, T1 = 1, T2 = 1, And in n >= 0 Under the condition of Tn+3 = Tn + Tn+1 + Tn+2

Give you an integer n, Please go back to n One tibonacci number Tn Value .

class Solution {
    
public:
    int tribonacci(int n) {
    
        if(n<=3)
        {
    
            if(n==0)
            {
    
                return 0;
            }
            else if(n<=2)
            {
    
                return 1;
            }
            else
            {
    
                return 2;
            }
        }
        else{
    
            int p=0,q=1,o=1,s=2;
            for(int i=4;i<=n;i++)
            {
    
                p=q;
                q=o;
                o=s;
                s=p+q+o;
            }
            return s;
        }
    }
};