1273. Delete Tree Nodes

A tree rooted at node 0 is given as follows:

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

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

Return the number of the remaining nodes in the tree.

class Solution {
    vector<vector<int>> g;
    pair<int, int> helper(int u, vector<int>& va) {
        int sum = 0, child = 0;
        for(auto& v : g[u]) {
            auto [s, c] = helper(v, va);
            sum += s;
            child += c;
        }
        
        return {sum + va[u], sum + va[u] ? child + 1 : 0};
    }
public:
    int deleteTreeNodes(int nodes, vector<int>& parent, vector<int>& value) {
        g = vector<vector<int>>(nodes);
        int root;
        for(int i = 0; i < nodes; i++)
            if(parent[i] != -1)
                g[parent[i]].push_back(i);
            else root = i;
        return helper(root, value).second;
    }
};