二叉树递归(DFS)

    1. /**
    2.  * Definition for a binary tree node.
    3.  * struct TreeNode {
    4.  *     int val;
    5.  *     TreeNode *left;
    6.  *     TreeNode *right;
    7.  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
    8.  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
    9.  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
    10.  * };
    11.  */
    12. class Solution {
    13. public:
    14.     bool isUnivalTree(TreeNode* root) {
    15.         int co_val=root->val;
    16.         bool result=dfs(root,co_val);
    17.         return result;
    18.     }
    19.     bool dfs(TreeNode* root,int co_val){
    20.         if(root==NULL){
    21.             return true;
    22.         }
    23.         if(root->val!=co_val){
    24.             return false;
    25.         }
    26.         bool a1=dfs(root->left,co_val);
    27.         bool a2=dfs(root->right,co_val);
    28.         return a1&&a2;
    29.     }
    30. };