Sword finger offer | Fibonacci sequence

Use recursion or loops .

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public int Fibonacci(int n) {
    
         if(n<=1){
    
             return n;
         }
         //return Fibonacci(n-1)+Fibonacci(n-2);
        int a=0,b=1;
        while(--n>0){
    
           int flag = a;
            a = b;
            b = flag+b;
        }
        return b;
    }