Does print statement in java effect any variables (without using increment)?

Question

I was trying out the leetcode problem here

the code i wrote is

public int toLeaf(TreeNode j){
        int ans=1;
        try{
            ans= Math.max(toLeaf(j.left),toLeaf(j.right))+1;
        }catch(Exception e){

        }
        return ans;
    }
    public int diameterOfBinaryTree(TreeNode root) {
        return toLeaf(root);
    }

which gave me wrong answer but as soon as added a print statment i got correct answers on the sample testcases

public int toLeaf(TreeNode j){
        int ans=1;
        try{
            ans= Math.max(toLeaf(j.left),toLeaf(j.right))+1;
        }catch(Exception e){

        }
        System.out.println(j.val+" "+ans);  //here
        return ans;
    }
    public int diameterOfBinaryTree(TreeNode root) {
        return toLeaf(root);
    }

what is the reason behind this? here is the screenshot rejected

Answer 1

The printing is not the cause of the different behaviour but the access of j.val is.

If you had proper null-checks in your code, e.g. if (j == null) { return 0; } in the beginning of the method this would not happen.

In the first snippet if you call the method with j = null you get an NPE in the try, catch it, ignore it and then return 1. The caller will get the 1, add 1 and then return 2.

In the second snippet if you call the method with j = null you once again get an NPE in the try, ignore it, then continue to the print which raises another NPE which is then thrown from the method and the recursive caller will catch it and not perform the ans = ... + 1 successfully but simply return 1.

Therefore you have a different behaviour between the two snippets. But this is entirely unrelated to printing itself.