814. Binary Tree Pruning

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* pruneTree(TreeNode* root) {
        if( root == NULL )return NULL;
        root->left = pruneTree( root->left );
        root->right = pruneTree( root->right );
        
        if( root->left == NULL && root->right == NULL && root-> val == 0 )return NULL;
        
        return root;
    }
};

 

后序遍历的变形