二叉树和递归

二叉树和递归

递归结构中必须包含两个部分，一个是递归终止条件，一个是递归过程。

/**
 * 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:
    int maxDepth(TreeNode* root) {
        int count=0;
        if(！root) 
            return count;
        if((root->left==NULL) && (root->right==NULL) && root) 
            return 1;
        return max(maxDepth(root->left)+1,maxDepth(root->right)+1);
    }
};

/**
 * 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:
    int minDepth(TreeNode* root) {
        if(!root) return 0;
        int left = minDepth(root->left);
        int right = minDepth(root->right);
        if(!left&&right) return right+1;
        if(!right&&left) return left+1;
        return min(left,right)+1;
    }
};

/**
 * 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* invertTree(TreeNode* root) {
        if(!root) return NULL;
        invertTree(root->left);
        invertTree(root->right);
        swap(root->left,root->right);
        return root;
    }
};

/**
 * 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:
    bool isSymmetric(TreeNode* root) {
        if(!root) return true;
        return dfs(root->left,root->right);
    }
    bool dfs(TreeNode* p,TreeNode* q){
        if(!p||!q)  return !p&&!q;
        return (p->val==q->val && dfs(p->left,q->right) && dfs(p->right,q->left));
    }
};

来源：CSDN

作者：XinyueRao

链接：https://blog.csdn.net/weixin_44289697/article/details/104532556