LeetCode刷题_c++版-199二叉树的右视图

/**
 * 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:
    //不管何种遍历，在同一层的情况下，总是先遍历左边的，再遍历右边的，因此只需要记录同一层最后遍历的节点
    void preOrder(vector<int>& result, TreeNode* root, int depth){
    
    
        if(root == NULL) return;
        //深度只会线性增长，不会跳跃式，新的深度的值只需放在数组最后即可
        if(depth > result.size()){
    
    
            result.push_back(root->val);
        }
        //同层，用新的值替换老的值
        else{
    
    
            result[depth - 1] = root->val;
        }
        preOrder(result, root->left, depth+1);
        preOrder(result, root->right, depth+1);
    }

    vector<int> rightSideView(TreeNode* root) {
    
    
        vector<int> result;
        //result.push_back(root->val);
        preOrder(result, root, 1);
        return result;
    }
};