Binary-Tree-Pruning

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题目地址

LeetCode#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.)

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

  题目要求去除值都为 0 的子树，照做就可以了。

解题代码

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/**
 * 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 {
    int getSubTreeValueSum(TreeNode *root) {
        if (!root) return 0;
        else return root->val + getSubTreeValueSum(root->left) + getSubTreeValueSum(root->right);
    }

public:
    TreeNode *pruneTree(TreeNode *root) {
        if (!root) return root;

        if (!getSubTreeValueSum(root->left)) {
            root->left = nullptr;
        }
        if (!getSubTreeValueSum(root->right)) {
            root->right = nullptr;
        }

        pruneTree(root->left);
        pruneTree(root->right);
        
        return root;
    }
};
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