leetcode: 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]]

广度优先遍历

/** * 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> > res;        if( root == NULL)            return res;        vector< int> cur;        queue< pair< TreeNode *, int> > q;        q.push( make_pair( root, 1));        int level = 1;        while( !q.empty()){            pair< TreeNode *, int> tmp = q.front();            q.pop();            if( tmp.first->left)                q.push( make_pair( tmp.first->left, tmp.second+1));            if( tmp.first->right)                q.push( make_pair( tmp.first->right, tmp.second+1));            if( tmp.second > level){                res.push_back( cur);                cur.clear();                ++level;            }            cur.push_back( tmp.first->val);        }        res.push_back( cur);        return res;    }};