Preface

Life is a journey , I am also a pedestrian .

/** * 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 {
    
public:
    bool dfs(TreeNode* root){
    
        if(!root) return false;         // Empty node means no 1, return false
        bool left = dfs(root->left);    // Judge whether there is 1
        bool right = dfs(root->right);  // Judge whether there is 1
        if(!left)   root->left = NULL;  // There is nothing on the left 1, Delete the left subtree 
        if(!right)  root->right = NULL; // There is nothing on the right 1, Then delete the right subtree 
        if(root->val != 1 && !left && !right)   
            return false;   // Not on the left 1 And there is no on the right 1 And I'm not 1, Should delete （ return false）
        return true;

    }
    TreeNode* pruneTree(TreeNode* root) {
    
        bool valid = dfs(root);
        if(!valid)
            root = nullptr; //  If there is no whole tree 1 Null node is returned 
        return root;
    }
};

/** * 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 {
    
public:
    bool seek(TreeNode* root)
    {
    
        if(root == NULL)
            return true;
        if(!seek(root->left))
            root->left = NULL;  //
        if(!seek(root->right))
            root->right = NULL;
        return root->val || root->left || root->right;// If there are children, it is not empty ( Children contain 1), Or this node is 1 Cannot delete this node 
    }
    TreeNode* pruneTree(TreeNode* root) {
    
        if(seek(root))
            return root;
        return NULL;
    }
};