递归这样理解，你将豁然开朗

递归这样理解，你将豁然开朗；

php版本

<?php 

$arr = array(
    array('id' => 1,'name' => 'A','parent_id'  => 0),
    array('id' => 2,'name' => 'B','parent_id'  => 0),
    array('id' => 3,'name' => 'A1','parent_id'  => 1),
    array('id' => 4,'name' => 'B1','parent_id'  => 2),
    array('id' => 5,'name' => 'A2','parent_id'  => 3),
    array('id' => 6,'name' => 'B2','parent_id'  => 4),
);

// 递归树
function deepFunction($arr,$id){
    $list = array();
    foreach ($arr as $key => $value) {
        if ($id == $value['parent_id']) {
            $child = deepFunction($arr,$value['id']);
            $value['child'] = $child;
            $list[] = $value;
        }
    }
    return $list;
}

$res = deepFunction($arr,0);
echo '<pre>';
var_dump($res);

方法1：无返回值法

 @GetMapping("/index6")
    public List<Integer> index6() {
        Integer id = 11;
        List<Category> categoryList = categoryMapper.selectList(null);
        // 声明引用返回值
        List<Integer> result = new ArrayList<>();
        checkCateData(categoryList, id, result);
         return result;
    }

    /**
     *
     * @param list  分类列表
     * @param id    查询id
     * @param result 搜集返回值(子分类所有id)
     * @return
     */
    private void checkCateData(List<Category> list, Integer id,List<Integer> result) {

        for (Category ca : list
        ) {
            if (ca.getFatherId().equals(id)){
                Integer ids = ca.getId();
                result.add(ids);
                checkCateData(list,ids,result);
            }
        }
    }

方法2：有返回值

 /**
     * 有返回值接收
     * @param categoryList
     * @param id
     * @return
     */
    private List<CategoryTreeVO> deepCategoryDataList(List<Category> categoryList, Integer id) {
        List<CategoryTreeVO> result = new ArrayList<>();
        for (Category cate : categoryList
        ) {
            if (cate.getFatherId().equals(id)) {
                CategoryTreeVO vo = new CategoryTreeVO();
                vo.setName(cate.getName());
                vo.setId(cate.getId());
                vo.setType(cate.getType());
                vo.setFatherId(cate.getFatherId());
                List<CategoryTreeVO> childList = deepCategoryDataList(categoryList, cate.getId());
                vo.setNodeCategoryList(childList);
                result.add(vo);
            }
        }
        return result;
    }

方法3：

  /**
     * 通过子集查询父级节点
     * @param list
     * @param parentId
     * @return
     */
    private List<Integer> queryFatherItem(List<Category> list, Integer parentId) {
        List<Integer> result = new ArrayList<>();
        for (Category cate : list
        ) {
            if (cate.getId().equals(parentId)) {
                result.add(cate.getId());
                List<Integer> integers = queryFatherItem(list, cate.getFatherId());
                result.addAll(integers);
            }
        }
        return result;
    }

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