Create number _of_employees_under_manager.java

employee_details.java

@@ -0,0 +1,98 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class NumberEmployeeUnderManager
+{
+	// A hashmap to store result. It stores count of employees
+	// under every employee, the count may by 0 also
+	static Map<String,Integer> result =
+							new HashMap<String, Integer>();
+
+	// Driver function
+	public static void main(String[] args)
+	{
+		Map<String, String> dataSet = new HashMap<String, String>();
+		dataSet.put("A", "C");
+		dataSet.put("B", "C");
+		dataSet.put("C", "F");
+		dataSet.put("D", "E");
+		dataSet.put("E", "F");
+		dataSet.put("F", "F");
+
+		populateResult(dataSet);
+		System.out.println("result = " + result);
+	}
+
+	// This function populates 'result' for given input 'dataset'
+	private static void populateResult(Map<String, String> dataSet)
+	{
+		// To store reverse of original map, each key will have 0
+		// to multiple values
+		Map<String, List<String>> mngrEmpMap =
+								new HashMap<String, List<String>>();
+
+		// To fill mngrEmpMap, iterate through the given map
+		for (Map.Entry<String,String> entry: dataSet.entrySet())
+		{
+			String emp = entry.getKey();
+			String mngr = entry.getValue();
+			if (!emp.equals(mngr)) // excluding emp-emp entry
+			{
+				// Get the previous list of direct reports under
+				// current 'mgr' and add the current 'emp' to the list
+				List<String> directReportList = mngrEmpMap.get(mngr);
+
+				// If 'emp' is the first employee under 'mgr'
+				if (directReportList == null)
+				{
+					directReportList = new ArrayList<String>();
+					// add a new entry for the mngr with empty directReportList
+					mngrEmpMap.put(mngr, directReportList);
+				}
+				directReportList.add(emp);
+			}
+		}
+
+		// Now use manager-Emp map built above to populate result
+		// with use of populateResultUtil()
+
+		// note- we are iterating over original emp-manager map and
+		// will use mngr-emp map in helper to get the count
+		for (String mngr: dataSet.keySet())
+			populateResultUtil(mngr, mngrEmpMap);
+	}
+
+	// This is a recursive function to fill count for 'mgr' using
+	// mngrEmpMap. This function uses memoization to avoid re-
+	// computations of subproblems.
+	private static int populateResultUtil(String mngr,
+							Map<String, List<String>> mngrEmpMap)
+	{
+		int count = 0;
+
+		// means employee is not a manager of any other employee
+		if (!mngrEmpMap.containsKey(mngr))
+		{
+			result.put(mngr, 0);
+			return 0;
+		}
+
+		// this employee count has already been done by this
+		// method, so avoid re-computation
+		else if (result.containsKey(mngr))
+			count = result.get(mngr);
+
+		else
+		{
+			List<String> directReportEmpList = mngrEmpMap.get(mngr);
+			count = directReportEmpList.size();
+			for (String directReportEmp: directReportEmpList)
+			count += populateResultUtil(directReportEmp, mngrEmpMap);
+
+			result.put(mngr, count);
+		}
+		return count;
+	}
+}

number _of_employees_under_manager.java

@@ -0,0 +1,99 @@
+// Java program to find number of persons under every employee
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class NumberEmployeeUnderManager
+{
+	// A hashmap to store result. It stores count of employees
+	// under every employee, the count may by 0 also
+	static Map<String,Integer> result =
+							new HashMap<String, Integer>();
+
+	// Driver function
+	public static void main(String[] args)
+	{
+		Map<String, String> dataSet = new HashMap<String, String>();
+		dataSet.put("A", "C");
+		dataSet.put("B", "C");
+		dataSet.put("C", "F");
+		dataSet.put("D", "E");
+		dataSet.put("E", "F");
+		dataSet.put("F", "F");
+
+		populateResult(dataSet);
+		System.out.println("result = " + result);
+	}
+
+	// This function populates 'result' for given input 'dataset'
+	private static void populateResult(Map<String, String> dataSet)
+	{
+		// To store reverse of original map, each key will have 0
+		// to multiple values
+		Map<String, List<String>> mngrEmpMap =
+								new HashMap<String, List<String>>();
+
+		// To fill mngrEmpMap, iterate through the given map
+		for (Map.Entry<String,String> entry: dataSet.entrySet())
+		{
+			String emp = entry.getKey();
+			String mngr = entry.getValue();
+			if (!emp.equals(mngr)) // excluding emp-emp entry
+			{
+				// Get the previous list of direct reports under
+				// current 'mgr' and add the current 'emp' to the list
+				List<String> directReportList = mngrEmpMap.get(mngr);
+
+				// If 'emp' is the first employee under 'mgr'
+				if (directReportList == null)
+				{
+					directReportList = new ArrayList<String>();
+					// add a new entry for the mngr with empty directReportList
+					mngrEmpMap.put(mngr, directReportList);
+				}
+				directReportList.add(emp);
+			}
+		}
+
+		// Now use manager-Emp map built above to populate result
+		// with use of populateResultUtil()
+
+		// note- we are iterating over original emp-manager map and
+		// will use mngr-emp map in helper to get the count
+		for (String mngr: dataSet.keySet())
+			populateResultUtil(mngr, mngrEmpMap);
+	}
+
+	// This is a recursive function to fill count for 'mgr' using
+	// mngrEmpMap. This function uses memoization to avoid re-
+	// computations of subproblems.
+	private static int populateResultUtil(String mngr,
+							Map<String, List<String>> mngrEmpMap)
+	{
+		int count = 0;
+
+		// means employee is not a manager of any other employee
+		if (!mngrEmpMap.containsKey(mngr))
+		{
+			result.put(mngr, 0);
+			return 0;
+		}
+
+		// this employee count has already been done by this
+		// method, so avoid re-computation
+		else if (result.containsKey(mngr))
+			count = result.get(mngr);
+
+		else
+		{
+			List<String> directReportEmpList = mngrEmpMap.get(mngr);
+			count = directReportEmpList.size();
+			for (String directReportEmp: directReportEmpList)
+			count += populateResultUtil(directReportEmp, mngrEmpMap);
+
+			result.put(mngr, count);
+		}
+		return count;
+	}
+}