从字符串中删除字符的所有匹配对

Question

I'm trying to make a code that deletes the repeated characters. For example - if we have a string "aabacdc" , we want to make it as "abd" . If the character exists twice in the string, then we delete both characters as we did in the above example. The 'a' occurs 3 times in our string, so we just deleted the 2 a and left 1 remaining.

What I'm trying to do in this code is use two nested for loops - first for loop to compare the first character with the other characters. If the character has a duplicate in the string, then just delete both the characters. How can I fix this code?

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

    StringBuilder str = new StringBuilder(str2);

    for (int k = 0; k < str.length() - 1; k++) {
        for (int i = 1; i < str.length() - 1; i++) {
            if (str.charAt(k) == str.charAt(i)) {
                str.deleteCharAt(k);
                str.deleteCharAt(i);
            } 
        }
    }

    System.out.println(str);
}

Answer 1

My interpretation of what you're trying to do based on your expected output is that you want to remove characters from the string 1 pair at a time. So if there is an odd number of a character in the string, 1 should remain, and if there's an even number 0 should remain.

Any time you're removing elements from a structure while you're iterating by index, you need to loop over the structure backwards, so that the index values don't shift as you delete elements. This means you should only delete elements which the outer loop is currently at, or has already seen (ie only delete elements at indexes >= i ).

Scanner input = new Scanner(System.in);
String str = input.nextLine();
StringBuilder sb = new StringBuilder(str);

for (int i = sb.length() - 2; i >= 0; i--) {
    for (int j = i + 1; j < sb.length(); j++) {
        if (sb.charAt(i) == sb.charAt(j)) {
            sb.deleteCharAt(j);
            sb.deleteCharAt(i);
            break;
        }
    }
}

System.out.println(sb);

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