binary_tree_level_order_ii
binary_tree_level_order_ii.cpp 源码
// 二叉树的层序遍历ii
#include "vector"
#include "queue"
#include "algorithm"
using namespace std;
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode() {}
TreeNode(int val) : val(val) {}
TreeNode(int val, TreeNode *left, TreeNode *right) : val(val), left(left), right(right) {}
};
class Solution {
public:
// 深度优先
vector<vector<int>> levelOrderBottom(TreeNode* root) {
vector<vector<int>> res;
helper(root, res, 0);
reverse(res.begin(), res.end());
return res;
}
void helper(TreeNode* root, vector<vector<int>>& res, int level) {
if (!root) {
return;
}
if (res.size() < level + 1) {
res.push_back(vector<int>{});
}
res[level].push_back(root->val);
helper(root->left, res, level + 1);
helper(root->right, res, level + 1);
}
// 广度优先
vector<vector<int>> levelOrderBottom1(TreeNode* root) {
vector<vector<int>> res;
if (!root) {
return res;
}
queue<TreeNode*> que;
que.push(root);
while (!que.empty()) {
int size = que.size();
vector<int> vals;
while (size-- > 0) {
TreeNode* node = que.front();
que.pop();
vals.push_back(node->val);
if (node->left) {
que.push(node->left);
}
if (node->right) {
que.push(node->right);
}
}
res.push_back(vals);
}
reverse(res.begin(), res.end());
return res;
}
};
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