Find.java

package arrays;

import java.util.ArrayList;

public class Find {
    public static void main(String[] args) {
        int [] arr = {2, 3, 4, 5, 4, 1, 6};
        System.out.println(find(arr,4,0));
        System.out.println(findIndex(arr,4,0));
        System.out.println(findIndexLast(arr,4,arr.length-1));
//        findAllIndex(arr, 4, 0);
//        System.out.println(list);
        ArrayList<Integer> ans = findAllIndex(arr, 4, 0,new ArrayList<>());
        System.out.println(ans);
        System.out.println(findAllIndex2(arr,4,0));

    }

    static boolean find(int []arr, int target, int index){
        if(index == arr.length){
            return false;
        }
        return(arr[index] == target|| find(arr,target,index+1));

    }

    static int findIndex(int []arr, int target, int index){
        if(index == arr.length){
            return -1;
        }
        if(arr[index] == target){
            return index;
        }else {
            return findIndex(arr, target, index + 1);
        }
    }

    static int findIndexLast(int []arr, int target, int index){
        if(index == 1){
            return -1;
        }
        if(arr[index] == target){
            return index;
        }else {
            return findIndexLast(arr, target, index - 1);
        }
    }


    static ArrayList<Integer> list = new ArrayList<>();
    static void findAllIndex(int []arr, int target, int index){
        if(index == arr.length){
            return;
        }
        if(arr[index] == target){
            list.add(index);
        }
        findAllIndex(arr, target, index + 1);
    }


    static ArrayList<Integer> findAllIndex(int []arr, int target, int index, ArrayList<Integer> list){
        if(index == arr.length){
            return list;
        }
        if(arr[index] == target){
            list.add(index);
        }
        return findAllIndex(arr, target, index + 1, list);
    }

    static ArrayList<Integer> findAllIndex2(int []arr, int target, int index){
        // not an optimised approach use the above one for that

        ArrayList<Integer> list = new ArrayList<>();

        if(index == arr.length){
            return list;
        }
        // This will contain answer for that function call only
        if(arr[index] == target){
            list.add(index);
        }
        ArrayList<Integer> ansFromBelowCalls = findAllIndex2(arr, target, index+1);

        list.addAll(ansFromBelowCalls);

        return list;
    }
}