199. 二叉树的右视图 - 力扣(LeetCode)
层次遍历,每次保存每一层的最后一个节点:
class Solution {
public:
vector<int> rightSideView(TreeNode* root) {
vector<int> res;
queue<TreeNode*> q;
if(!root) return res;
q.push(root);
while(!q.empty()){
int n = q.size();
for(int i = 0; i < n; ++i){
auto p = q.front();
q.pop();
if(i == n-1) res.push_back(p->val);
if(p->left) q.push(p->left);
if(p->right) q.push(p->right);
}
}
return res;
}
};
为了方便输出,push的时候可以先push右边,再push左边:
class Solution {
public:
vector<int> rightSideView(TreeNode* root) {
vector<int> res;
queue<TreeNode*> q;
if(!root) return res;
q.push(root);
while(!q.empty()){
res.push_back(q.front()->val);
int n = q.size();
for(int i = 0; i < n; ++i){
auto p = q.front();
q.pop();
if(p->right) q.push(p->right);
if(p->left) q.push(p->left);
}
}
return res;
}
};