蓝桥杯大纲大题通用样题“Luhn算法”

Luhn算法

 

 

 

import java.util.Scanner;

class BigNum{
    
    int []num;  //位数
     
    public BigNum(){
        num = new int[21];
        for(int i = 0; i < num.length; i++) {
            num[i] = 0;
        }
    }
    
    public BigNum(int n) {
        num = new int[n];
    }
    public boolean full() {
        for(int i = 0; i < num.length; i++) {
            if(num[i] != 9) {
                return false;
            }
        }
        return true;
    }
     
    public void plusOne() {
        int tag = 0;    //从最后一位开始加，如果其9，将其变为0，另高一位加一，
                        //如果高一位是9，其变为0，高一位加一一次类推直到全为9
                        //tag == 0说明从第0位开始
        if(num[tag]!=9) {
            num[tag]++;
            return;
        }else {
            if(full())  return; //如果全为9则溢出
             
            //关键算法。。进位操作
            while(true) {
                num[tag]=0;
                tag++;
                if(num[tag] != 9) {
                    num[tag]++;
                    return;
                }
            }
        }
    }
    public void show() {
        for(int i = num.length-1; i >-1; i--) {
            System.out.print(num[i]);
        }
        System.out.println();
    }
    
    
    
    public void setElem(int pos, int n) {
        num[pos] = n;
    }
     
    public boolean isLuhn() {
        int OddPlus=0;  //奇数位和，在数组中为偶数位和
        int EvenPlus=0; //偶数位和，在数组中为奇数位和
        
        for(int i = 0; i < num.length; i+=2) {
            OddPlus+=num[i];
        }
        
        int num2=-999;
        for(int i = 1; i < num.length; i+=2) {
            num2 = num[i]*2;
            if (num2>9) {
                num2-=9;
            }
            EvenPlus+=num2;
        }
        OddPlus+=EvenPlus;
        if (OddPlus%10==0) {
            return true;
        }
        return false;
    }
}


public class ComformCreditCard {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scanner = new Scanner(System.in);
        
        //输入字符串
        String str = scanner.next();
        //从字符串提取数字
        BigNum bNum = new BigNum(str.length());
        
        
        
        //放入数据
        for (int j = 0; j < str.length(); j++) {
            bNum.setElem(j, str.charAt(j)-48);
        }
        
        if (bNum.isLuhn()) {
            System.out.print("成功");
        }else {
            System.out.print("失败");
        }
        
        
        
        
    }

}