如何返回 Java 中创建的数组？

Question

In this program, I'm supposed to count the amount of times the letters 'A','B' and 'C' are in the string and return that as an array. The input is ABBACCCCAC and I'm supposed to get an output of [3, 2, 5] but I'm getting [1, 1, 2, 2, 1, 2, 3, 4, 3, 5]

import java.util.Arrays;
public class HelloWorld{

 public static void main(String []args){
    String str = "ABBACCCCAC";
    int[] arr = new int[str.length()];
    int acount = 0, bcount = 0, ccount = 0;
    
    for(int i =0; i<str.length();i++){
        if(str.charAt(i) == 'A'){
            acount++;
            arr[i] = acount;
        }
        else if(str.charAt(i) == 'B'){
            bcount++;
            arr[i] = bcount;
        }
        else if(str.charAt(i) == 'C'){
            ccount++;
            arr[i] = ccount;
        }
    }
    System.out.print(Arrays.toString(arr));
 }
}

Answer 1

You were close. Just change your array size to 3 and the indiced to 0,1, and 2.

   String str = "ABBACCCCAC";
    int[] arr = new int[3];
    int acount = 0, bcount = 0, ccount = 0;
    
    for(int i =0; i<str.length();i++){
        if(str.charAt(i) == 'A'){
            acount++;
            arr[0] = acount;
        }
        else if(str.charAt(i) == 'B'){
            bcount++;
            arr[1] = bcount;
        }
        else if(str.charAt(i) == 'C'){
            ccount++;
            arr[2] = ccount;
        }
    }
    System.out.print(Arrays.toString(arr));

Your could also just increment the array locations directly.

arr[0]++; // like this.

Answer 2

Right now, you are assigning the counts to the array at each step of the counting, whereas you should have done this at the end of the count. Also, note that you created an array the same length of the string, rather than the expected 3 .

You should just move the creation of the array to the end, with an array creation expression:

String str = "ABBACCCCAC";
int acount = 0, bcount = 0, ccount = 0;

for(int i =0; i<str.length();i++){
    if(str.charAt(i) == 'A'){
        acount++;
    }
    else if(str.charAt(i) == 'B'){
        bcount++;
    }
    else if(str.charAt(i) == 'C'){
        ccount++;
    }
}

int[] arr = new int[] { acount, bcount, ccount }; // <--- here!
System.out.print(Arrays.toString(arr));