题解 | #求二叉树的层序遍历#

使用队列求解

 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 
     * @return int整型vector<vector<>>
     */
    vector<vector<int> > levelOrder(TreeNode* root) {
        // write code here
        vector<vector<int>> res;
        queue<TreeNode*> levelNode;
        int cnt = 0;
        if(root != NULL){
            levelNode.push(root);
            cnt = 1;
        }
        
        while(levelNode.size() != 0){
            int cntTmp = 0;
            vector<int> level;
            for(int i=0; i<cnt; i++){
                TreeNode* treeNode = levelNode.front();
                level.push_back(treeNode->val);
                if(treeNode->left != NULL){
                    levelNode.push(treeNode->left);
                    cntTmp++;
                }
                if(treeNode->right != NULL){
                    levelNode.push(treeNode->right);
                    cntTmp++;
                }
                levelNode.pop();
            }
            cnt = cntTmp;
            res.push_back(level);
        }
        
        return res;
    }
};