如何返回元素个数？ [英] How to return the number of elements?

问题描述

我必须编写一个函数，该函数将整数列表作为参数&返回列表中小于1的整数的数目。到目前为止，我拥有的一个函数只是返回列表中有多少个整数。我不确定应该在哪里/如果要放置if语句和计数器以仅返回小于1的整数。

I have to write a function that takes a list of integers as a parameter & returns the number of integers from the list that are less than 1. What I have so far is a function that just returns how many integers in the list. I am not sure where/if I'm supposed to put a if statement and counter to only return how many integers are less than 1.

-export([num/1]).

num([]) -> 0 ;
num(L) -> num(L,0).

num([],Len) -> Len;
num([_|T],Len) ->
    num(T,Len+1).

推荐答案

您的代码已经差不多了。要学习的关键技能： guard

Your code is almost there. Key skill to learn: guard

-export([num/1]).

num([]) -> 0;
num(NUMS) ->
        num(NUMS, 0).

num([H|L], Count) when H < 1 ->  %% use of guard
        num(L, Count+1);
num([_|L], Count) ->
        num(L, Count);
num([], Count) ->
        Count.

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