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$ curl repovive.com/roadmaps/dynamic-programming/dp-on-trees/sum-of-distances-implementation

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$ curl repovive.com/roadmaps/dynamic-programming/dp-on-trees/sum-of-distances-implementation

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LeetCode 834 Sum of Distances in Tree - Implementation - DP on Trees | Dynamic Programming | Repovive

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Dynamic Programming21 sections · 918 units60h total

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LeetCode 834 Sum of Distances in Tree - Implementation

The formula

function sumOfDistances(n, edges)
    // Build adjacency list
    // Pass 1 (down): compute count[v] and sum[v]
    dfs_down(0, -1)

    // Pass 2 (up): propagate answers
    ans[0] = sum[0]
    dfs_up(0, -1)

    return ans

Two passes using the rerooting technique. One pass down collects subtree info, one pass up distributes answers.

Time: $O(n)$ . Space: $O(n)$ .