Java程序在字符串中打印第一个非重复字符

Question

public static void main(String[] args) {
        String str = "XXYZZA";

        char[] a = str.toCharArray();
        int count=0;
        for (int i = 0; i < a.length; i++) 
        {
            if (a[i] == a[i++]) 
            {
                count++;

            } 
            else
                System.out.println(a[i++]);

        }

    }

the print statement in the "else" part is not being executed. the desired output should be

Y
A

Answer 1

Ok, first and for-most, proper indentations please, helps out a lot to understand the code.

Secondly, if (a[i] == a[i++]) is not the right way to go because of 2 reasons

1. your for loop will start skipping i values since you are using a unary operator , which will act directly on the operand .
2. ArrayIndexOutOfBounds : once your i reaches its max value of a.length - 1 your test condition i++ will try to access the element at index a.length , which, as you might have guessed it, does not exist.

What you need is some sort of sorting algorithm without actually saving the sorted sequence.

Answer 2

Try like this, may help you

  public static void main(String[] args) {
    String str = "XXYZZA";

    char[] a = str.toCharArray();
    HashSet<Character> set = new HashSet<>();
    set.add( a[0]);
    for (int i = 1; i < a.length; i++)
    {
      if (!set.contains(a[i]) && (i+1 == a.length || a[i] != a[i+1]))
      {
        System.out.println(a[i]);
      }
      set.add(a[i]);

    }