[leetcode]Binary Tree Level Order Traversal

简单题

/**
 * Definition for binary tree
 * 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> > ans;
        if(root == nullptr) return ans;
        queue<TreeNode* > que[2];
        int mark = 0;
        que[0].push(root);
        while(!que[mark].empty()) {
            int next = (mark + 1) % 2;
            vector<int> level;
            while(!que[mark].empty()) {
                TreeNode* tmp = que[mark].front() ; que[mark].pop();
                level.push_back(tmp -> val);
                if(tmp -> left) que[next].push(tmp -> left);
                if(tmp -> right) que[next].push(tmp -> right);
            }
            ans.push_back(level);
            mark = next;
        }
        return ans;
    }
};