功能变成无限循环

Question

我有一个我用PHP编写的函数的问题.如您所见,该函数使用自身返回值的数组.

    public function getRepeat($day = "array")
{
    if ($day == 'array')
    {//Return an array with the repeated days as values
        foreach (array(1,2,3,4,5,6,0) as $value) 
        {
            if ($this->getRepeat($value))
            {
                $returnArray[] = $value;
            }
        }
        return $returnArray;
    }
    else if (in_array($day, array(1,2,3,4,5,6,0) ))
    {
        if ($day == 1)
            return $this->repeat1;
        if ($day == 2)
            return $this->repeat2;
        if ($day == 3)
            return $this->repeat3;
        if ($day == 4)
            return $this->repeat4;
        if ($day == 5)
            return $this->repeat5;
        if ($day == 6)
            return $this->repeat6;
        if ($day == 0)
            return $this->repeat0;
    }
}

一旦它自己调用每个变量就会变成无限循环.

是什么导致这个？

Answer 1

您必须始终考虑分两部分编写递归函数:

1. 基本情况 - 在这一点上你停止递归并返回一个值(即列表为空)
2. 递归情况 - 如何再次调用函数以及输入与前一个调用的不同之处(即,您是否发送了列表的尾部)

确保这两个规则保持应该导致递归函数,在输入有效的情况下终止该函数.

这是一个递归的解决方案 - 但它是在Java :)

    public static void main(String[] args) {

    List<Integer> testVals = new ArrayList<Integer>();
    testVals.add(0);
    testVals.add(1);
    testVals.add(2);
    testVals.add(3);
    testVals.add(4);
    testVals.add(5);

    List<Integer> toMatch = new ArrayList<Integer>(testVals);

    List<Integer> matches = new ArrayList<Integer>();

    repeatRec(testVals, matches, toMatch);

    System.out.println("Matches " + matches);
}

public static void repeatRec(List<Integer> toTest, List<Integer> matches, List<Integer> toMatch) {


    if (toTest.isEmpty()) {
        //we are done
        return;
    } else {

        Integer head = toTest.get(0);

        if (toMatch.contains(head)) {
            matches.add(head);

        }

        //could have else here if we're only interested in the first match
        repeatRec(toTest.subList(1, toTest.size()), matches, toMatch);
    }
}