Recursive search without using loops or any other java methods (not using math.max etc.) and only using two parameters: the array and an index?

Question

This is a homework assignment and I'm having trouble figuring out what I'm doing wrong. I am supposed to write a method that returns the max int from an array of ints without using a loop or any other methods such as Math.max etc. I wrote a method that can do it with a while loop but I am having trouble figuring out what is wrong with my recursive search. I keep getting 0 when doing the recursive search.

public class RecursiveGetMax {
public static void main(String[] args) {
    int [] arr = {1,3,7,5,4};
    System.out.println("The max int using a loop is: " + loopMax(arr,0));
    System.out.println("The max int using a recursive search is: " + recursiveMax(arr,0));
}
public static int loopMax(int[] arr, int index) {
    int ret = 0;
    int maxSoFar = 0;
    while (index < arr.length-1) {
        if(arr[index] >= maxSoFar) {
            maxSoFar = arr[index];
        }
        ++index;
    }
    if (index == arr.length-1) {
        ret = maxSoFar;
    }
    return ret;
}
public static int recursiveMax(int[]arr, int index) {
    int maxSoFar = 0;
    int ret = 0;
    if (index > arr.length-1) {
        ret = maxSoFar;
    }
    else {
        if (arr[index] >= maxSoFar){
            maxSoFar = arr[index];
        }
        recursiveMax(arr,index + 1);
    }
    return ret;
}
}

Please follow up link > http://stackoverflow.com/questions/19590242/finding-max-value-in-an-array-using-recursion — Rahul Patel, Dec 08 '16 at 06:17
Possible duplicate of [What is a debugger and how can it help me diagnose problems?](http://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — Raedwald, Dec 08 '16 at 08:05

Scary Wombat · Accepted Answer · 2016-12-08T06:52:53.173

try this code The main problem was then maxSoFar was getting overwritten and your recursive call did not return its value

static int maxSoFar = Integer.MIN_VALUE;  // set to a very small number
public static void main (String [] args) throws Exception 
{
    int [] arr = {1,3,7,5,4};

    System.out.println("The max int using a recursive search is: " + recursiveMax(arr,0));  // pass it in

}

public static int recursiveMax(int[]arr, int index) {  

    if (index > arr.length-1) {
        return maxSoFar;
    }
    else {
        if (arr[index] >= maxSoFar){
            maxSoFar = arr[index];
        }
        return recursiveMax(arr,index + 1);
    }
}

Edit

Changed to use static variable due to OP's comments

The only parameters i'm allowed to use for this assignment are int[] arr and int index. I am not allowed to pass maxSoFar. — JohnnyDanger113, Dec 08 '16 at 06:51

score 0 · Answer 2 · answered Dec 08 '16 at 06:19

look at the max function..

public class Snippet {
    public static void main(String[] args) {
        int arr[] = {3,5,6,2,8,6,5,1};
        System.out.println(max(arr, 1, arr[0]));
    }

    public static int max(int arr[], int i, int max){
        if(i < arr.length){
            max = Math.max(arr[i], max);
            return max(arr, i+1, max);
        }
        return max;
    }
}

the key point is you need to carry all require data, while recurse

Recursive search without using loops or any other java methods (not using math.max etc.) and only using two parameters: the array and an index?

2 Answers2