花花酱 LeetCode 1273. Delete Tree Nodes

A tree rooted at node 0 is given as follows:

• The number of nodes is nodes;
• The value of the i-th node is value[i];
• The parent of the i-th node is parent[i].

Remove every subtree whose sum of values of nodes is zero.

After doing so, return the number of nodes remaining in the tree.

Example 1:

Input: nodes = 7, parent = [-1,0,0,1,2,2,2], value = [1,-2,4,0,-2,-1,-1]
Output: 2

Constraints:

• 1 <= nodes <= 10^4
• -10^5 <= value[i] <= 10^5
• parent.length == nodes
• parent[0] == -1 which indicates that 0 is the root.

Solution: Inorder Traversal

For each node, return the sum of all its subtrees and number of nodes including itself after removal.

Time complexity: O(n)
Space complexity: O(n)