思路: 利用 BFS 进行层次遍历,记录下每层的最后一个元素
class Solution {
public:
vector<int> rightSideView(TreeNode* root) {
if (!root) return {};
vector<int> res;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
int sz = q.size();
for (int i = 0; i < sz; i++) {
auto node = q.front(); q.pop();
if (node->left) q.push(node->left);
if (node->right) q.push(node->right);
// 添加当前层的最后1个节点到解中
if (i == sz - 1) res.emplace_back(node->val);
}
}
return res;
}
};