寻找子字符串/按行读文件

1. 问题一 from sg
   其功能为从字符串str中返回从beginStr开始到endStr结束的中间子串。如str=”abcdefmsgleisw” beginStr=”cd” endStr=”ei” 结果为 “efmsgl“

public static String substr(String str, String begin, String end){
        if(str.length()<=0){
            return null;
        }
        int i= str.indexOf(begin);
        //System.out.println(i);

        int j= str.indexOf(end);
        if(i==-1 || j==-1 || j<=i){  // begin/end不存在 || end在begin之前
            return null;
        }
        i=i+begin.length();
        return str.substring(i, j);
    }

2. 问题二 from sg

   
   image.png

public static class Pro{
        int  count;
        float price;
        public Pro(int  count,float price){
            this.count=count;
            this.price=price;
        }
    }

    public static void getAvgPrice() throws Exception{
        String path="log.txt";
        HashMap<String,Pro> hashMap=new HashMap<>();
        FileInputStream fileInputStream=new FileInputStream(path);
        InputStreamReader in=new InputStreamReader(fileInputStream,"UTF-8");
        BufferedReader bf=new BufferedReader(in);
        try {
            String content=bf.readLine();
            while (content!=null){
                float price=Float.parseFloat(content.split(" ")[4]);
                String name=content.split(" ")[3];
                if(hashMap.get(name)!=null){
                    hashMap.get(name).price+=price;
                    hashMap.get(name).count++;
                }else if(hashMap.get(name)==null){
                    hashMap.put(name,new Pro(1,price));
                }
                content=bf.readLine();
            }
            for(String key:hashMap.keySet()){
                System.out.println(key+" avg price is:"+hashMap.get(key).price/hashMap.get(key).count);
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            fileInputStream.close();
            in.close();
            bf.close();
        }
    }

3. 问题三 from ks

// 数组中每走m步，删除一个元素，数组走到最后则再回到数组首部，直到剩下最后一个元素输出;
    public static void delItem(){
        int[] arr={1,2,3,4,5,6};int m=2;
        int len=arr.length;
       //for(int i=0;i<len-1;i++){ //要找出len-1个元素，下标从0开始则i<len-1
        int i=0;
        int k=0;
        int j=0;
        while (i<len-1){
            if(k==m){
                arr[j%len]=-1;
                i++;
                k=0;
                System.out.printf(j%len+"");
            }
            if(arr[(++j)%len]!=-1) {
                k++;
            }
        }
        System.out.printf("\n");
        for (int f:arr){
            System.out.println(f);
        }
    }