LeetCode617. 合并二叉树

题目

class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if(!t1 && !t2) return NULL;
        if(t1 == NULL&& t2 != NULL) return t2;
        if(t1 != NULL&& t2 == NULL) return t1;
        TreeNode* node = new TreeNode(t1->val + t2->val);;
        //指针赋值使用错误TreeNode* node; node->val = t1->val + t2->val;
        node->left = mergeTrees(t1->left,t2->left);
        node->right = mergeTrees(t1->right,t2->right);
        return node;
    }
};

需要查看C++ primer, 复习指针使用

class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if(root1 == NULL) return root2;
        if(root2 == NULL) return root1;
        
        TreeNode *root = new TreeNode(root1->val + root2->val);
        root->left = mergeTrees(root1->left,root2->left);
        root->right = mergeTrees(root1->right,root2->right);
        return root;

    }
};

迭代法 层次遍历

class Solution {
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if(root1 == NULL) return root2;
        if(root2 == NULL) return root1;
        
        //两个根都不为空
        queue<TreeNode*>que;
        que.push(root1);que.push(root2);
        //TreeNode *node = new TreeNode;
        while(!que.empty()){
            auto t1 = que.front();que.pop();
            auto t2 = que.front();que.pop();
            t1->val +=  t2->val;
            if(t1->left != NULL && t2->left != NULL){
                que.push(t1->left);
                que.push(t2->left);
            }
            if(t1->right != NULL && t2->right != NULL){
                que.push(t1->right);
                que.push(t2->right);
            }
            if(t1->left == NULL ){
                t1->left = t2->left;
            }

            if(t1->right == NULL){
                t1->right = t2->right;
            }
        }
        return root1;
    }
};