LeetCode 124 Binary Tree Maximum Path Sum - Implementation

Pseudocode:

maxPath := -infinity

function dfs(v)
    if v is null then
        return 0
    leftMax := max(dfs(v.left), 0)
    rightMax := max(dfs(v.right), 0)
    maxPath := max(maxPath, v.val + leftMax + rightMax)
    return v.val + max(leftMax, rightMax)

Call dfs(root), then return maxPath. Time: $O(n)$ (visit each node once). Space: $O(h)$ for recursion stack where $h$ is tree height. On balanced trees, $h = \log n$. On skewed trees, $h = n$.