1080. Insufficient Nodes in Root to Leaf Paths

Given the root of a binary tree and an integer limit, delete all insufficient nodes in the tree simultaneously, and return the root of the resulting binary tree.

A node is insufficient if every root to leaf path intersecting this node has a sum strictly less than limit.

A leaf is a node with no children.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    TreeNode* helper(TreeNode* node, int limit, int sum) {
        sum += node->val;
        bool hasChild = node->left or node->right;
        
        if(!hasChild) return sum < limit ? nullptr : node;
        
        if(node->left) node->left = helper(node->left, limit, sum);
        if(node->right) node->right = helper(node->right, limit, sum);
        
        if(hasChild and !(node->left or node->right)) return nullptr;
        return node;
    }
public:
    TreeNode* sufficientSubset(TreeNode* root, int limit) {
        return helper(root, limit, 0);
    }
};