论算法重要性 递归返回值null

刘嘉先
java
算法, 递归
阅读量
文章目录
  1. 1. 问题分析
  2. 2. 解决方法

遇到一个树形结构的数据处理，需要用到递归算法，想想也简单，就写呗，经过调试，一旦进入递归返回值就被清空了

问题分析

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private Map<String,BigDecimal> getAbnormalsLevel(String checkId, Integer itemId,Map<String,BigDecimal> levelMap) {
        List<String> list = tZhiKangCheckMapper.selectCheckDataByFatherItemId(checkId,itemId);
        if(list.isEmpty()){
            //查不到数据 说明没有子节点了;
            Map<String,Object> result = tZhiKangCheckMapper.selectAbnormalsLevel(checkId,itemId);
            Assert.notNull(result, "查询异常数据错误");

            BigDecimal abnormalsNewCount = new BigDecimal(result.get("abnormalsCount").toString());
            BigDecimal abnormalsNewLevel = new BigDecimal(result.get("abnormalsLevel").toString());

            if(levelMap==null){
                levelMap = new HashMap<>();
                BigDecimal abnormalsCount = BigDecimal.ZERO;
                BigDecimal abnormalsLevel = BigDecimal.ZERO;
                levelMap.put("abnormalsCount",abnormalsCount);
                levelMap.put("abnormalsLevel",abnormalsLevel);
            }

            BigDecimal abnormalsCount = new BigDecimal(levelMap.get("abnormalsCount").toString());
            BigDecimal abnormalsLevel = new BigDecimal(levelMap.get("abnormalsLevel").toString());

            levelMap.put("abnormalsCount",abnormalsCount.add(abnormalsNewCount));
            levelMap.put("abnormalsLevel",abnormalsLevel.add(abnormalsNewLevel));
        }else{
            //查到数据递归继续遍历
            for(String fatherItemIdStr : list){
                Integer fatherItemId = Integer.valueOf(fatherItemIdStr);
                getAbnormalsLevel(checkId,fatherItemId,levelMap);
            }
        }
        return levelMap;
    }

当有子节点的时候进入循环递归，进入后levelMap的值就被清空了，没有达到累加效果

解决方法

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private Map<String,BigDecimal> getAbnormalsLevel(String checkId, Integer itemId,Map<String,BigDecimal> levelMap) {
        List<String> list = tZhiKangCheckMapper.selectCheckDataByFatherItemId(checkId,itemId);
        if(list.isEmpty()){
            //查不到数据 说明没有子节点了;
            Map<String,Object> result = tZhiKangCheckMapper.selectAbnormalsLevel(checkId,itemId);
            Assert.notNull(result, "查询异常数据错误");

            BigDecimal abnormalsNewCount = new BigDecimal(result.get("abnormalsCount").toString());
            BigDecimal abnormalsNewLevel = new BigDecimal(result.get("abnormalsLevel").toString());

            if(levelMap==null){
                levelMap = new HashMap<>();
                BigDecimal abnormalsCount = BigDecimal.ZERO;
                BigDecimal abnormalsLevel = BigDecimal.ZERO;
                levelMap.put("abnormalsCount",abnormalsCount);
                levelMap.put("abnormalsLevel",abnormalsLevel);
            }

            BigDecimal abnormalsCount = new BigDecimal(levelMap.get("abnormalsCount").toString());
            BigDecimal abnormalsLevel = new BigDecimal(levelMap.get("abnormalsLevel").toString());

            levelMap.put("abnormalsCount",abnormalsCount.add(abnormalsNewCount));
            levelMap.put("abnormalsLevel",abnormalsLevel.add(abnormalsNewLevel));
        }else{
            //查到数据递归继续遍历
            for(String fatherItemIdStr : list){
                Integer fatherItemId = Integer.valueOf(fatherItemIdStr);
                levelMap = getAbnormalsLevel(checkId,fatherItemId,levelMap);
            }
        }

        return levelMap;
    }

[u]将递归后的值重新赋给返回值即可，就这么个小毛病折腾了好久[/u]

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levelMap = getAbnormalsLevel(checkId,fatherItemId,levelMap);
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