Populating Next Right Pointers in Each Node II

/**
 * 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) {
        if(!root) return;
        queue< pair<TreeLinkNode*,int> > q;
        q.push(pair<TreeLinkNode*,int>(root,0));
        pair<TreeLinkNode* ,int> prev;
        while(!q.empty()){
            pair<TreeLinkNode*,int> temp=q.front();
            q.pop();
            if(prev.first!=NULL&& prev.second==temp.second)
                prev.first->next=temp.first;
            prev=make_pair(temp.first,temp.second);
            if(temp.first->left) q.push(pair<TreeLinkNode*,int>(temp.first->left,temp.second+1));
            if(temp.first->right) q.push(pair<TreeLinkNode*,int>(temp.first->right,temp.second+1));
        }
    }
};