Question

例如，我想查找数字123900148中重复1的次数它必须被写入2次，但每次都会得到错误的值

Scanner input = new Scanner(System.in);
@author Başar Ballıöz

int counter = 0;
int repeat;
int tmp;


System.out.print("Enter A Number: ");
tmp = input.nextInt();
String number = Integer.toString(tmp);


System.out.print("Enter A Number You Want To Find: ");
repeat = input.nextInt();


for (int i = 0; i < number.length() - 1 ; i++) {    

    if (number.substring(i , i+1).equals(repeat))

    counter++;
}

System.out.println(repeat + " number " + counter + " repeated.");

我希望看到如下输出：

number : 134211
number i want to find how many times repeated: 1
your number has repeated 3 times

Answer 1

您正在将String（由number.substring(i , i+1返回）与Integer进行比较，因此当然它将始终返回false。

比较两个int或两个String。由于您本质上是比较两个数字，因此比较int会更有效。

for (int i = 0; i < number.length(); i++) {    
    if (Character.getNumericValue(number.charAt(i)) == repeat) {
        counter++;
    }
}

Answer 2

  Scanner input = new Scanner(System.in);

    int counter = 0;
    int repeat;
    int tmp;

    System.out.print("Enter A Number: ");
    tmp = input.nextInt();
    String number = Integer.toString(tmp);

    System.out.print("Enter A Number You Want To Find: ");
    repeat = input.nextInt();

    while (tmp > 0) {

        if (tmp % 10 == repeat) {
            counter++;               
        }
        tmp = tmp/10;
    }

    System.out.println(number + " number " + counter + " repeated.");

Answer 3

您正在通过String将Integer与equals进行比较，因此无法获得预期的结果。而是在比较之前将整数转换为字符串：

 if (number.substring(i , i+1).equals(String.valueOf(repeat)))

此外，您可以将String.valueOf(repeat)的结果缓存到for循环之前的变量中，以防止在每次循环中构造字符串对象。

Answer 4

尝试一下。我添加了一些有用的输出，以便您可以看到如何对其进行索引。

import java.util.Scanner;
import java.util.Map;
import java.util.HashMap;

public class CountChars {

    public static void main(String [] args) {

        Scanner input = new Scanner(System.in);

        System.out.print("Enter A String: ");
        Map<String, Integer> map = indexString(input.nextLine());

        while (true) {
            System.out.print("Enter A Character You Want To Count (ENTER to exit): ");
            String repeat = input.nextLine();
            if (repeat == null || repeat.isEmpty()) {
                break;
            }
            System.out.println(String.format("'%s' was repeated %d time(s).", repeat, (map.containsKey(repeat)) ? map.get(repeat):Integer.valueOf(0)));
        }
    }

    private static Map<String, Integer> indexString(String s) {
        Map<String, Integer> map = new HashMap<>();
        System.out.println(String.format("'%s' has %d characters.  Indexing now.", s, s.length()));
        for (int i = 0; i < s.length() ; i++) {
            String c = String.valueOf(s.charAt(i));
            if (!map.containsKey(c)) {
                map.put(c, 0);
                System.out.println(String.format("Indexing %s", c));
            }
            System.out.print(String.format("Incrementing '%s' from %d ", c, map.get(c)));
            map.put(c, map.get(c) + 1);
            System.out.println(String.format("to %d.", map.get(c)));
        }
        return map;
    }

}

设定数字重复多少次的程序

4 个答案: