102. Binary Tree Level Order Traversal & 107. Binary Tree Level Order Traversal II & 103. Binary Tre

最新推荐文章于 2019-11-25 21:41:40 发布

nemoyy

最新推荐文章于 2019-11-25 21:41:40 发布

阅读量238

点赞数

本文链接：https://blog.youkuaiyun.com/nemoyy/article/details/68954220

版权

102. Binary Tree Level Order Traversal

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],

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        queue<TreeNode *> q;
        vector<vector<int>> v;
        
        if(!root) return v;
        
        q.push(root);
        while(!q.empty()){
            int levelsize = q.size();
            vector<int> subv;
            for(int i = 0; i < levelsize;i++){
                TreeNode * p = q.front();
                q.pop();
                if(p->left) q.push(p->left);
                if(p->right) q.push(p->right);
                subv.push_back(p->val);
            }
            v.push_back(subv);
        }
        return v;
    }
};

107. Binary Tree Level Order Traversal II

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

For example:
Given binary tree [3,9,20,null,null,15,7],

return its bottom-up level order traversal as:

[
  [15,7],
  [9,20],
  [3]
]

reverse(v.begin(),v.end());

103. Binary Tree Zigzag Level Order Traversal

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between).

For example:
Given binary tree [3,9,20,null,null,15,7],

return its zigzag level order traversal as:

[
  [3],
  [20,9],
  [15,7]
]

class Solution {
public:
    vector<vector<int>> zigzagLevelOrder(TreeNode* root) {
        queue<TreeNode *> q;
        vector<vector<int>> v;
        
        if(!root) return v;
        
        q.push(root);
        bool level = true;
        while(!q.empty()){
            int levelsize = q.size();
            vector<int> subv;
            for(int i = 0; i < levelsize;i++){
                TreeNode * p = q.front();
                q.pop();
                if(p->left) q.push(p->left);
                if(p->right) q.push(p->right);
                subv.push_back(p->val);
            }
            if(!level)reverse(subv.begin(),subv.end()); 
            v.push_back(subv);
            level = !level;
        }
        return v;
    }
};