Leetcode_102

层序遍历

#include <iostream>
#include <vector>
#include <queue>
using namespace std;
struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x):val(x),left(NULL),right(NULL) {}
};
vector<vector<int>> levelOrder(TreeNode* root) {
    vector<vector<int>> res;
    if(root==NULL)
        return res;
    queue<pair<TreeNode*,int>> q;
    q.push(make_pair(root,0));
    while(!q.empty())
    {
        TreeNode *node = q.front().first;
        int level = q.front().second;
        q.pop();
        if(level == res.size())
            res.push_back(vector<int>());
        res[level].push_back(node->val);
        if(node->left)
            q.push(make_pair(node->left,level+1));
        if(node->right)
            q.push(make_pair(node->right,level+1));
    }
    return res;

}