CareerCup

Hierarchical data structure:

package com.cracking.google;

public class EnumParentChild {
	
	static enum Vehicle {
		car(null,1),
			toyota(car,11),
				camry(toyota,111),
				coroloa(toyota,112),
			honda(car,12),
		track(null,2),
			GMC(track,21);
		
		Vehicle(Vehicle parent,int value) {
			this.parent = parent;
			this.value = value;
		}
		
		public Vehicle parent;
		public int value;
	}
	

	public static void main(String[] args) {
		System.out.println(Vehicle.GMC + " " + Vehicle.GMC.value);
		System.out.println(Vehicle.GMC.parent + " " + Vehicle.GMC.parent.value);
	}

}

Output:
GMC 21
track 2

not sure how this design will scale, but anyway, I understood we have:
- enum integer values that are hirarchical, e.g. each decimal place represents a hirarchy
- there is a way to lookup the textual representation of the enum value e.g. there is a hashtable with integer key and text representation value
- you want the parent-key of a key? that is integer division by 10
- I wonder what you do if there are more then 10 children .. but anyway, here the code

unordered_map<int, string> enums_{{1, "car"}, {11, "toyota"}, {111, "prius"} /*, ... */ }; 

	pair<int, string> get_parent(int value) {
		if(value >= 10) {
			auto it = enumns_.find(value/10);
			if(it != enums.end()) {
				return it->second;
			}
		}
		throw "error, has no parent (?)";
	}

Its a composite design pattern, we are supposed to reuse the parent value.

/**
 * give an enum, where each element has a parent-children relationship, and children's expression is the value of parent append an index, such as
 * enum vehicle {
 *          car = 1
 *              toyota = 11
 *                   camry = 111
 *                   corolla = 112
 *              honda = 12
 *         truck = 2
 *              GMC = 21
 * }
 *
 */
public class ParentChild {

    public enum Vehicle {
        CAR("1",null),
            TOYATA("1",CAR),
                CAMERY("1",TOYATA),
                CORALLA("2",TOYATA),
            HONDA("2",CAR),
        TRUCK("2",null),
            GMC("1",TRUCK)
        ;

        String value;
        Vehicle(String val, Vehicle parent) {
            if(parent!=null) {
                this.value = parent.value+val;
            } else {
                this.value = val;
            }

        }

        @Override
        public String toString() {
            return name()+":"+value;
        }
    }

    public static void main(String[] args) {
        System.out.println(Vehicle.TOYATA);
        System.out.println(Vehicle.CORALLA);
        System.out.println(Vehicle.GMC);
    }
}