void find(TreeNode x, List<Integer> list, int level){
        if(x==null)return;
        if(list.size()==level)list.add(x.val);
        find(x.left, list, level+1);
        find(x.right, list, level+1);
    }
We get left side view of binary tree and return last element.
src/problems/medium/FindLeftMostElement.java