LeetCode/102.binary-tree-level-order-traversal.cpp at master · AlienYou/LeetCode · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
/*
 * @lc app=leetcode id=102 lang=cpp
 *
 * [102] Binary Tree Level Order Traversal
 *
 * https://leetcode.com/problems/binary-tree-level-order-traversal/description/
 *
 * algorithms
 * Medium (56.08%)
 * Likes:    4199
 * Dislikes: 102
 * Total Accepted:    772.1K
 * Total Submissions: 1.4M
 * Testcase Example:  '[3,9,20,null,null,15,7]'
 *
 * Given a binary tree, return the level order traversal of its nodes' values.
 * (ie, from left to right, level by level).
 *
 *
 * For example:
 * Given binary tree [3,9,20,null,null,15,7],
 *
 * ⁠   3
 * ⁠  / \
 * ⁠ 9  20
 * ⁠   /  \
 * ⁠  15   7
 *
 *
 *
 * return its level order traversal as:
 *
 * [
 * ⁠ [3],
 * ⁠ [9,20],
 * ⁠ [15,7]
 * ]
 *
 *
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        if (root == nullptr)
            return vector<vector<int>>();
        queue<TreeNode*> que;
        que.push(root);
        vector<vector<int>> res;
        while (!que.empty()) {
            vector<int> curLevel;
            int size = que.size();
            for (int i = 0; i < size; ++i) {
                TreeNode* cur = que.front();
                que.pop();
                curLevel.push_back(cur->val);
                if (cur->left)
                    que.push(cur->left);
                if (cur->right)
                    que.push(cur->right);
            }
            if (size > 0)
                res.push_back(curLevel);
        }
        return res;
    }

    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> st;
        while (!st.empty() || root) {
            if (root) {
                st.push(root);
                root = root->left;
            } else {
                root = st.top();
                st.pop();
                result.push_back(root->val);
                root = root->right;
            }
        }
        return result;
    }

    vector<int> inorderTraversal1(TreeNode* root) {
        vector<int> result;
        core(root, result);
        return result;
    }

    void core(TreeNode* root, vector<int>& result) {
        if (root == nullptr)
            return;
        core(root->left, result);
        result.push_back(root->val);
        core(root->right, result);
    }
};
// @lc code=end