java - 计算整数数组中的重复元素

Question

我有一个整数数组crr_array，我想对重复出现的元素进行计数。首先，我读取数组的大小并使用从控制台读取的数字对其进行初始化。在数组 new_array 中，我存储了重复的元素。数组 times 存储元素连续出现的次数。然后，我尝试搜索重复序列并以特定格式打印它们。但是，它不起作用。

// Get integer array size
Scanner input = new Scanner(System.in);
System.out.println("Enter array size: ");
int size = input.nextInt();

int[] crr_array = new int[size];
int[] new_array= new int[size];
int[] times = new int[size];

// Read integers from the console
System.out.println("Enter array elements: ");
for (int i = 0; i < crr_array.length; i++) {
    crr_array[i] = input.nextInt();
    times[i] = 1;
}

// Search for repeated elements
for (int j = 0; j < crr_array.length; j++) {
    for (int i = j; i < crr_array.length; i++) {
        if (crr_array[j] == crr_array[i] && j != i) {
            new_array[i] = crr_array[i];
            times[i]++;
        }
    }
}



//Printing output
for (int i = 0; i <  new_array.length; i++) {
    System.out.println("\t" + crr_array[i] + "\t" +  new_array[i] + "\t" + times[i]);

}

我希望输出看起来像这样:

There are <count_of_repeated_element_sequences> repeated numbers 
<repeated_element>: <count> times
...

例如:

There are 3 repeated numbers:
22: 2 times
4: 3 times
1: 2 times

如何找到重复元素及其计数？如何打印它们如上所示？

Answer 1

这类问题可以通过字典(Java中的HashMap)轻松解决。

  // The solution itself 
  HashMap<Integer, Integer> repetitions = new HashMap<Integer, Integer>();

  for (int i = 0; i < crr_array.length; ++i) {
      int item = crr_array[i];

      if (repetitions.containsKey(item))
          repetitions.put(item, repetitions.get(item) + 1);
      else
          repetitions.put(item, 1);
  }

  // Now let's print the repetitions out
  StringBuilder sb = new StringBuilder();

  int overAllCount = 0;

  for (Map.Entry<Integer, Integer> e : repetitions.entrySet()) {
      if (e.getValue() > 1) {
          overAllCount += 1;

          sb.append("\n");
          sb.append(e.getKey());
          sb.append(": ");
          sb.append(e.getValue());
          sb.append(" times");
      }
  }

  if (overAllCount > 0) {
      sb.insert(0, " repeated numbers:");
      sb.insert(0, overAllCount);
      sb.insert(0, "There are ");
  }

  System.out.print(sb.toString());