LeetCode-Populating Next Right Pointers in Each Node

有点类似于层级遍历，用两个数组保存上下两层的结点即可！

同样的代码两道题目都可以过！

/**
 * Definition for binary tree with next pointer.
 * struct TreeLinkNode {
 *  int val;
 *  TreeLinkNode *left, *right, *next;
 *  TreeLinkNode(int x) : val(x), left(NULL), right(NULL), next(NULL) {}
 * };
 */
class Solution {
public:
    void connect(TreeLinkNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<TreeLinkNode*> > level(2);
        int pre = 0;
        int cur = 1;
        if (root == NULL) {
            return;
        }
        level[cur].push_back(root);
        while (!level[cur].empty()) {
            pre = !pre;
            cur = !cur;
            level[cur].clear();
            for (size_t i = 0; i < level[pre].size(); ++i) {
                if (i == level[pre].size() - 1) {
                    level[pre][i]->next = NULL;
                }
                else {
                    level[pre][i]->next = level[pre][i + 1];
                }
                if (level[pre][i]->left != NULL) {
                    level[cur].push_back(level[pre][i]->left);
                }
                if (level[pre][i]->right != NULL) {
                    level[cur].push_back(level[pre][i]->right);
                }
            }
        }
    }
};