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Leetcode Problem 834. Sum of Distances in Tree

834. Sum of Distances in Tree

Leetcode Solutions

Subtree Sum and Count Approach

  1. Root the tree at an arbitrary node (e.g., node 0).
  2. Perform a post-order traversal to compute count and stsum for each node.
  3. Initialize ans[root] with stsum[root].
  4. Perform a pre-order traversal where for each parent-child pair (parent, child), compute ans[child] using the formula ans[child] = ans[parent] - count[child] + (n - count[child]).
  5. Return the ans array containing the sum of distances for each node.
UML Thumbnail

Naive Pairwise Distance Summation

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