C++二叉树的直径与合并详解

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
/**
 * 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:
    int res=0; //定义一个全局变量
    int depth(TreeNode* root){  //求深度
        if(root==nullptr)  return 0;
        int L=depth(root->left); 
        int R=depth(root->right);
        res=max(res,L+R);
        return max(L,R)+1;
    }
    int diameterOfBinaryTree(TreeNode* root) {
        depth(root);
        return res;
    }
};

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
/**
 * 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:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        // 判空
        if(root1==nullptr) return root2;
        if(root2==nullptr) return root1;
        // 修改了t1的数值和结构
        root1->val+=root2->val;
        root1->left=mergeTrees(root1->left,root2->left);
        root1->right=mergeTrees(root1->right,root2->right);
        return root1;
    }
};