116.connect.cpp

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* left;
    Node* right;
    Node* next;

    Node() : val(0), left(NULL), right(NULL), next(NULL) {}

    Node(int _val) : val(_val), left(NULL), right(NULL), next(NULL) {}

    Node(int _val, Node* _left, Node* _right, Node* _next)
        : val(_val), left(_left), right(_right), next(_next) {}
};
*/

class Solution {
public:
    Node* connect(Node* root) {
        if(!root) return root;
        queue<Node*> queue;
        queue.push(root);
        while(!queue.empty()){
            int size = queue.size();
            for(int i = 0; i < size; i++){
                Node* cur = queue.front();
                queue.pop();
                if(i < size - 1)
                    cur->next = queue.front();
                if(cur->left) queue.push(cur->left);
                if(cur->right) queue.push(cur->right);
            }
        }
        return root;
    }
};