菲薄数列

/**
 * Created by wangchaomac on 2017/3/13.
 */
/*
1.斐波那契数列
**/
function fbnq(sqIndex){
    var firstNo = 1;
    var secondNo = 1;
    if( sqIndex < 2 ) {
        if( sqIndex < 0) {

            return 'error input param';
        }
        return 1;
    }

    var fbnqNo = -1;

    for(var fbnqIndex = 2; fbnqIndex < sqIndex ; fbnqIndex ++) {

        fbnqNo = firstNo + secondNo ;
        firstNo = secondNo ;
        secondNo =  fbnqNo ;
    }

    return fbnqNo;

}
alert(fbnq(4));