First Index

Base Case

public class FirstIndex {
    public static void main(String[] args) {
        int[] arr = new int[]{0, 1, 2, 3, 4, 5};
        int num = 2;
        int ans = firstIndex(arr, num, 0);
        System.out.println(ans);
    }

    private static int firstIndex(int[] arr, int ele, int idx) {
        // base case
        if (idx == arr.length)
            return -1;
        
        if (arr[idx] == ele) {
            return idx;
        }
        // faith
        int val = firstIndex(arr, ele, idx + 1);

        return val;
    }
}