Leetcode[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,#,#,15,7},

3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:

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

思路： 使用层序遍历，一层一层的出队，并将节点值放入数组中；

代码C++：

/**
 * 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) {
        vector<vector<int> > res;
        vector<int> nums;
        if(root == NULL) return res;
        queue<TreeNode *> que;
        TreeNode *p = root;
        que.push(p);
        while(!que.empty()){
            int queSize = que.size();
            nums.resize(0);
            for(int i = 0; i < queSize; i++){
                p = que.front();
                nums.push_back(p->val);
                if(p->left) que.push(p->left);
                if(p->right) que.push(p->right);
                que.pop();
            }
            res.push_back(nums);
        }
        return res;
    }
};

有问题，来一起讨论吧~