LeetCode-199. Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Example:

Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

题解：

bfs遍历，每次找出每层最右边的数放进去。

class Solution {
public:
  vector<int> rightSideView(TreeNode* root) {
    vector<int> ans;
    if (root == NULL) {
      return ans;
    }
    queue<TreeNode*> q;
    q.push(root);
    int size = 1;
    while (q.empty() == false) {
      TreeNode *p = q.front();
      q.pop();
      if (p->left != NULL) {
        q.push(p->left);
      }
      if (p->right != NULL) {
        q.push(p->right);
      }
      size--;
      if (size == 0) {
        ans.push_back(p->val);
        size = q.size();
      }
    }
    return ans;
  }
};