Find number of Employees Under every Employee - GeeksforGeeks
Given a dictionary that contains mapping of employee and his manager as a number of (employee, manager) pairs.
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Given a dictionary that contains mapping of employee and his manager as a number of (employee, manager) pairs.
{ "A", "C" },
{ "B", "C" },
{ "C", "F" },
{ "D", "E" },
{ "E", "F" },
{ "F", "F" }
In this example C is manager of A,
C is also manager of B, F is manager
of C and so on.
Write a function to get no of employees under each manager in the hierarchy not just their direct reports. It may be assumed that an employee directly reports to only one manager.
1. Create a reverse map with Manager->DirectReportingEmployee
combination. Off-course employee will be multiple so Value
in Map is List of Strings.
"C" --> "A", "B",
"E" --> "D"
"F" --> "C", "E", "F"
2. Now use the given employee-manager map to iterate and at
the same time use newly reverse map to find the count of
employees under manager.
Let the map created in step 2 be 'mngrEmpMap'
Do following for every employee 'emp'.
a) If 'emp' is not present in 'mngrEmpMap'
Count under 'emp' is 0 [Nobody reports to 'emp']
b) If 'emp' is present in 'mngrEmpMap'
Use the list of direct reports from map 'mngrEmpMap'
and recursively calculate number of total employees
under 'emp'.
A trick in step 2.b is to use memorization(Dynamic programming) while finding number of employees under a manager so that we don’t need to find number of employees again for any of the employees.
// 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>();// 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>(); directReportList.add(emp); // Replace old value for 'mgr' with new // directReportList mngrEmpMap.put(mngr, directReportList); } } // 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; }