public void map(Object key, Text value, Context context)
				throws IOException, InterruptedException {
			String airport = value.toString();
			airport = airport.replace("\n", "").replace("\r", "");

			String minCenter = "";
			double minDis = Double.MAX_VALUE;
			for (String center : centerList) {
				if (center.equalsIgnoreCase(airport))
					continue;
				String matrixKey = center.compareTo(airport) < 0 ? center + ","
						+ airport : airport + "," + center;
				double dis = matrix.containsKey(matrixKey) ? matrix
						.get(matrixKey) : 0;
				if (dis <= minDis) {
					minDis = dis;
					minCenter = center;
				}
			}

			context.write(new Text(minCenter), new Text(airport));
		}