Find the vertical sum of a binary tree?

Short answer: void VerticalSum(TreeNode root, int hd, Dictionary<int, int> map) { if (root == null) return; VerticalSum(root.left, hd - 1, map); if (map.ContainsKey(hd)) map[hd] += root.val; else map[hd] = root.val; VerticalSum(root.right, hd + 1, map); } Dictionary<int, int> GetVerticalSum(TreeNode root) { var map = new Dictionary<int, int>(); VerticalSum(root, 0, map); return map; } Explanation: Use horizontal distance (hd)…

Explain a bit more

from root; sum values of nodes at each hd. Follow on:

Example code

void VerticalSum(TreeNode root, int hd, Dictionary<int, int> map) { if (root == null) return; VerticalSum(root.left, hd - 1, map); if (map.ContainsKey(hd))
map[hd] += root.val; else map[hd] = root.val; VerticalSum(root.right, hd + 1, map); }
Dictionary<int, int> GetVerticalSum(TreeNode root) {
var map = new Dictionary<int, int>(); VerticalSum(root, 0, map); return map;
} Explanation: Use horizontal distance (hd) from root; sum values of nodes at each hd. Follow on:

Real-world example (ShopNest)

In coding rounds, state complexity aloud, write a clear ShopNest-flavored example (orders, carts), then handle edge cases (empty list, null, overflow).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.