image.png

思路:

  • 还是标准的层次遍历二叉树，如果当前层大小为0，说明已经遍历到最右边那个节点了
  • 队列的大小就是当前层的大小，这是理解的关键所在

代码：

  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.     vector<int> rightSideView(TreeNode* root) {
  15.         vector<int> right_view_vals;
  16.         if(!root) {
  17.             return right_view_vals;
  18.         }
  20.         queue<TreeNode*> q;
  21.         q.push(root);
  23.         while (!q.empty()) {
  24.             // cur_level_size 就是 q 的大小，这一点很关键
  25.             int cur_level_size = q.size();
  26.             while (cur_level_size--) {
  27.                 TreeNode* node = q.front();
  28.                 if (cur_level_size == 0) {
  29.                     right_view_vals.push_back(node->val);
  30.                 }
  32.                 q.pop();
  33.                 if (node->left) {
  34.                     q.push(node->left);
  35.                 }
  36.                 if (node->right) {
  37.                     q.push(node->right);
  38.                 }
  39.             }
  40.         }
  42.         return right_view_vals;
  43.     }
  44. };