递归地找到Java数组中数字的总和

Question

I understand that finding the sum of numbers in an array is much more easily done through iteration instead of recursion, but if I were to use recursion to write such a function, what would be wrong with this code?

public static double sum (double[] a) {
    if (a.length == 0)
        return 0.0;
    else{
        return sumHelper (a, 1, a[0]);
    }
}
private static double sumHelper (double[] a, int i, double result) {
    if (i < a.length) {
        result = result + sumHelper (a, i + 1, result);
    }
    return result;
}

Everything runs without errors, yet does not return the correct sum when I test it out.

Answer 1

Initialise the value of i to 0 because you are passing 1. or try this one

public static void main(String args[]){
    double a[]=new double[10];
    a[0]=123;
    a[1]=123;
    a[2]=123;
    a[3]=123;
    a[4]=123;
    a[5]=123;
    a[6]=123;
    a[7]=123;
    a[8]=123;
    a[9]=123;
    System.out.println(sum(a));
}

Answer 2

public class RecursiveSum {
    public static void main(String[] args) {
        System.out.println(sum(new double[] {1,3,4,5}));
    }

    public static double sum(double[] a) {
        if (a.length == 0)
            return 0.0;
        else{
            return sumHelper(a, 0);
        }
    }

    private static double sumHelper(double[] a, int i) {
        if(a.length - 1 == i){
            return a[i];
        }else{
            return  a[i] + sumHelper(a, i + 1);
        }
    }
}

Answer 3

You have problem with main method declaration:

public static void main(String args[]){
        double a[]=new double[10];
        a[0]=123;
        a[1]=123;
        a[2]=123;
        a[3]=123;
        a[4]=123;
        a[5]=123;
        a[6]=123;
        a[7]=123;
        a[8]=123;
        a[9]=123;
        System.out.println(sum(a));
    }

Answer 4

If you just use a single method to recursively sum all the numbers in an array, then this is how you would go. public static void main(String[] args) {

      double a[]=new double[6]; //initialize it
        a[0]=1; //fill it with values
        a[1]=2;
        a[2]=3;
        a[3]=4;
        a[4]=5;
        a[5]=6;

        System.out.println(sum(a, a.length-1)); //call the method and print as well

}

public static double sum( double arr[], int n ) { 
      if (n < 0) {
        return 0;
      } else{
        return arr[n] + sum(arr, n-1); //magic 
      }
    }