Binary Tree Pruning

We are given the head node root of a binary tree, where additionally every node's value is either a 0 or a 1.

Return the same tree where every subtree (of the given tree) not containing a 1 has been removed.

(Recall that the subtree of a node X is X, plus every node that is a descendant of X.)

Example 1: Input: [1,null,0,0,1] Output: [1,null,0,null,1]

Explanation: Only the red nodes satisfy the property "every subtree not containing a 1". The diagram on the right represents the answer.

Example 2: Input: [1,0,1,0,0,0,1] Output: [1,null,1,null,1]

Example 3: Input: [1,1,0,1,1,0,1,0] Output: [1,1,0,1,1,null,1]

Solution: Divide and Conqur

    TreeNode* pruneTree(TreeNode* root) {
        if (!root) return NULL;
        root->left = pruneTree(root->left);
        root->right = pruneTree(root->right);

        if (!root->left && !root->right) {
            return root->val == 0 ? NULL : root;
        }
        return root;
    }