js斐波那契数列求和

一、递归算法
 function recurFib(n) {
  if (n < 2) {
    return n;
  }
  else {
    return recurFib(n-1) + recurFib(n-2);
  }
 }

  alert(recurFib(10));//将显示55







二、动态规划法
  function dynFib(n) {
    var val = [];
    for (var i = 0; i <= n; ++i) {
     val[i] = 0;
    }
    if (n == 1 || n == 2) {
      return 1;
    }
    else {
      val[1] = 1;
      val[2] = 2;
      for (var i = 3; i <= n; ++i) {
        val[i] = val[i-1] + val[i-2];
      }
      return val[n-1];
    }
  }
  alert(dynFib(10));//将显示55



三、迭代法

 function iterFib(n){
  var last=1;
  var nextlast=1;
  var result=1;
  for(var i=2;i<n;++i){
    result=last+nextlast;
    nextlast=last;
    last=result;
  }
  return result;
 }

 alert(iterFib(10));//将显示55