**Prerequisites:** Binary trees, Binary tree traversal.

**Problem:** Given a binary tree, find the sum of leaves at deepest level.

**Solution Approach:** A simple preorder traversal can be used to solve this problem. This idea is to visit the tree downwards while keeping track of level, *maxlevel* and *sum_at_deepest_level*. Whenever we find a level deeper than current *maxlevel*, we update the *sum_at_deepest_level* with node value at this level otherwise if the current level is equal to *maxlevel*, we add the current node’s value to *sum_at_deepest_level*.

Finally, *sum_at_deepest_level* will have a sum of nodes’ values which are at the deepest level.

**Time Complexity:** O(N) as we need to explore each node at least once.

**Space complexity:** O(1), as we don’t need any significant extra space.