helium_2 Python2 template is broken: the first line of the input should be interpreted before the mapreduce (as in the other templates), so that the mapper receives the set name as the key instead of the line number..
leewangzhong Someone copy-pasted a wordcount solution without thinking through the differences between the necessary structure for a wordcount and for an intersection. Line numbers are significant in wordcount, but not this problem.
The Python version also asks much harder questions of the solver than the other languages, which only ask you to complete an equality check.
The output format is also wrong, and you must either edit the class or bypass it to get the correct answer.
Here is a template to use. It is still not as easy as the versions in the other three languages.
# This template is based on the framework supplied for a similar challenge, in a Coursera Data Science course: https://www.coursera.org/course/datasci # And the code supplied here: https://github.com/uwescience/datasci_course_materials/blob/master/assignment3/wordcount.py import json import sys from collections import OrderedDict class MapReduce: def __init__(self): self.intermediate = OrderedDict() self.result = [] def emitIntermediate(self, key, value): self.intermediate.setdefault(key, []) self.intermediate[key].append(value) def emit(self, value): self.result.append(value) def execute(self, data, mapper, reducer): for line in data: record = json.loads(line) mapper(record) for key in self.intermediate: reducer(key, self.intermediate[key]) return self.result mapReducer = MapReduce() def mapper(record): key = record["key"] value = record["value"] # ADD THE REQUIRED LOGIC BELOW # You may need to add some lines for the mapper logic to work # At the end, you need to complete the emit intermediate step mapReducer.emitIntermediate(?, ?) def reducer(key, list_of_values): # ADD THE REQUIRED LOGIC BELOW # You may need to add some lines for the reducer logic to work # At the end, you need to complete the emit step mapReducer.emit(?) if __name__ == '__main__': inputData = [] nr, ns = map(int, raw_input().split()) for i in range(nr): k = int(raw_input()) inputData.append(json.dumps({"key":k,"value":"R"})) for i in range(ns): k = int(raw_input()) inputData.append(json.dumps({"key":k,"value":"S"})) result = mapReducer.execute(inputData, mapper, reducer) for n in result: print n
maxim_musin Regarding the Java version. Could you explain why JSONObject and some other wrappers are used?
I have tried to simplify the initial version provided: https://ideone.com/eF2Xzf
hiresh Please mention the significance of LinkedHashMap in the template of java, why do we need the insertion order maintained in the inputdata json
k1e13 Although R and S are mentioned as set, it would still be better to explicitly state that the numbers for each of the collections won't be repeated. Also, line 176: "intermediate.put(key,temp);" (in Java code) is confusing, please remove it from the template. Rest the code is elegant, beautiful and self-explainatory to say the least. Kudos to team Hackerrank for introducing such a challenge. :)
johntron Think carefully about the keys used for the map; you can easily create intermediate values which already indicate the sets each integer appears in - no need to do this in the reduce.
decuqa There is a mistake within the Python code: pref using sys.stdin.read().splitlines() into the for loop (reading JSON file) not to add \n or EOF into the keys.
Moghaak This code will only work provided, R and S are set themselves. But I was wondering if we get to code the entire map and reduce method by ourselves then this would have been pretty good challanges. But all I see here is fill in one value which is very simple!
mohana_krishna08 @Moghaak yes you are right but we should understand the program flow and map reduce paradigm to insert that value
decuqa In fact you have to do more than just fill the gaps. You should add a few code before mapReducer.emitIntermediate(?, ?) and mapReducer.emit((?, ?)). The idea is that you have to map in some way to facilitate the reduce operation after. In fact reduce() exploits previously created dictionary (map) and performs checks to produce the final "reduced" dictionary.
Hope it's helpful!
ziqilin import json import sys from collections import OrderedDict class MapReduce: def init(self): self.intermediate = OrderedDict() self.result = [] self.r=0 def emitIntermediate(self, key, value): self.intermediate.setdefault(key, []) self.intermediate[key].append(value)
def emit(self, value): self.result.append(value) def execute(self, data, mapper, reducer): for line in data: record = json.loads(line) mapper(record) for key in self.intermediate: reducer(key, self.intermediate[key]) for item in self.result: print item,mapReducer = MapReduce()
def mapper(record): # print record key = record["key"] value = record["value"] # ADD THE REQUIRED LOGIC BELOW # You may need to add some lines for the mapper logic to work # At the end, you need to complete the emit intermediate step if key!=1: if key<=mapReducer.r: mapReducer.emitIntermediate(value,'r' ) else: mapReducer.emitIntermediate(value,'q' ) else: mapReducer.r=int(value.split()[0])
def reducer(key, list_of_values): # ADD THE REQUIRED LOGIC BELOW # You may need to add some lines for the reducer logic to work # At the end, you need to complete the emit step if 'r' in list_of_values and 'q' in list_of_values: mapReducer.emit(key)
if name == 'main': inputData = [] counter = 0 for line in sys.stdin: counter += 1 inputData.append(json.dumps({"key":counter,"value":line})) mapReducer.execute(inputData, mapper, reducer) mapReducer.execute(inputData, mapper, reducer)
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