814. Binary Tree Pruning

题目描述：

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]

Note:

The binary tree will have at most 100 nodes.
The value of each node will only be 0 or 1.

解题思路：

树一般用递归的方法。

代码：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     TreeNode* pruneTree(TreeNode* root) {
13         if (root == NULL)
14             return NULL;
15         root->left = pruneTree(root->left);
16         root->right = pruneTree(root->right);
17         if (root->val == 0 && root->left == NULL && root->right == NULL) {
18             free(root);
19             return NULL;
20         }
21         return root;
22     }
23 };

转载于:https://www.cnblogs.com/gsz-/p/9385599.html

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