[daily question] first day

️ Author： intellectuals
️ Personal blog ： Old nine CSDN Blog
Personal famous saying ： Uncontrollable things Optimistic face
Series column ： A daily topic

choice

Character Is a wrapper class , Cannot store string constants ,String Sure ,StringBuffer need new Objects can only be used ,Vector Is a collection

Method rewrite ： There is an inheritance relationship , The method parent class required by the subclass cannot meet , The permission size of subclass method override must be greater than that of the parent class , Everything else is the same

Principles of structured programming ： modularization , The top-down , Progressive refinement

The member variable is not initialized and defaults to 0

java The remainder can take decimals ,C Language doesn't work

Only static methods can be accessed with class names

Programming questions 1

The grouping method can be sorted from small to large , Then take the first and last two to form a group
The formula ：arr.len-2*(i+1)

public class test1 {
    
    public static void main(String[] args) {
    
        Scanner scan = new Scanner(System.in);
        while (scan.hasNextInt()) {
    
            int n = scan.nextInt();
            int[] array = new int[3 * n];
            long sum = 0;
            for (int i = 0; i < 3 * n; i++) {
    
                array[i] = scan.nextInt();
            }

            Arrays.sort(array);

            for (int i = 0; i < n; i++) {
    
                sum += array[array.length - 2 * (i + 1)];
            }
            System.out.println(sum);
        }
    }
}

Programming questions 2

1. Traverse str2 This string , Put the corresponding characters in hash[]
2. Traverse str1, find == 0 Is the character you want

public class test1 {
    
    public static void main(String[] args) {
    
        Scanner scan = new Scanner(System.in);
        String str1 = scan.nextLine();
        String str2 = scan.nextLine();

        HashMap<Character,Integer> map = new HashMap();
        for(int i = 0;i<str2.length();i++){
    
            if(map.get(str2.charAt(i)) == null){
    
                map.put(str2.charAt(i),1);
            }else{
    
                map.put(str2.charAt(i),map.get(str2.charAt(i))+1);
            }
        }
        String ret = "";
        for(int i = 0;i< str1.length();i++){
    
            if(map.get(str1.charAt(i)) == null){
    
                ret += str1.charAt(i);
            }
        }
        System.out.println(ret);
    }
}

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It's not easy to code words , Everyone's support is my driving force to stick to it
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