斐波那契递归算法

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<?php
//1 1 2 3 5 8 13 21....斐波那契数列
function fbnq($n){
  if($n<=2){
    return 1;
  }
  return fbnq($n-1)+fbnq($n-2);
}
echo fbnq(6);

//调用流程
//fbnq(6)=>fbnq(5)+fbnq(4)
//fbnq(5)=>fbnq(4)+fbnq(3)
//fbnq(4)=>fbnq(3)+fbnq(2)
//fbnq(3)=>fbnq(2)+fbnq(1)
//fbnq(3)=>1+1
//然后再递归算回去