Find the vertical sum of a binary tree?

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.

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