不錯的題 貌似有人頭條被問過

class cmp {
  public:
	bool operator()(const pair<int, int>& n1, const pair<int, int>& n2) const {
		return n1.first > n2.first;
	}
};

class Solution {
public:
	vector<int> smallestRange(vector<vector<int> >& nums) {
		priority_queue< pair<int, int>, vector< pair<int, int> >, cmp > q;
		vector< int > ptrs( nums.size(), 0 );
		vector<int> ret;
		int mx = -1e6;
		
		for (int i = 0; i < nums.size(); i++) {
			q.push( make_pair( nums[i][0], i ) );
			mx = max(mx, nums[i][0]);
        }

		int n = nums.size();
		int ans = mx - q.top().first;
        ret.push_back(q.top().first);
        ret.push_back(mx);
		
		while ( q.size() ) {
			pair<int, int> tp = q.top();
            // cout << "tp.first" << tp.first << endl;
			q.pop();
            
            if (mx - tp.first < ans) {
                ret[0] = tp.first;
                ret[1] = mx;
                ans = ret[1] - ret[0];
            }
            
            ptrs[ tp.second ] ++;
            if (ptrs[tp.second] >= nums[tp.second].size()) break;
            q.push( make_pair( nums[tp.second][ ptrs[ tp.second ] ], tp.second ) );
            
            mx = max(mx, nums[tp.second][ ptrs[ tp.second ] ]);
				
		}
		
		return ret;
	}
};