Finding the mode of n numbers

Question

I'm trying to write a program, in which the user gives n numbers and the program has to find out which number is being repeated the most. for example for numbers : 4 5 5 1 3 1 1 7 1 the answer is 1 I'm a beginner by the way, so that's why most of the answers which were already on the site didn't suit me. I'd be very thankful.

Either show your code, and describe the specific issue or this will be closed as a duplicate of http://stackoverflow.com/questions/9316352/how-do-i-find-the-mode-of-an-array — Thomas Matthews, Dec 01 '14 at 20:29
@ThomasMatthews: That question asks about a sorted array, and I've adjusted its title to reflect that. — Benjamin Lindley, Dec 01 '14 at 20:41
So, I didn't list all the results from the search: https://www.google.com/search?q=stackoverflow+c%2B%2B+find+mode&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb — Thomas Matthews, Dec 01 '14 at 20:50
@Sara, you might want to use a `std::vector` as per my answer. — Andreas DM, Dec 01 '14 at 21:26

midor · Answer 1 · 2014-12-01T21:16:13.473

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Use a hashmap (unordered_map) to count the occurrences of the numbers, then search the maximum occurrence count in the hashmap.

edited Dec 01 '14 at 21:16

answered Dec 01 '14 at 20:30

midor

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The overhead of hashing is not required here; an `std::map` would suffice. – cdhowie Dec 01 '14 at 20:40
Using a std::map increases the algorithmic complexity to O(n log n), whereas using a hashmap is O(n). n O(1) inserts and one O(n) search vs n O(log n) inserts. Have you ensured, that insertion into std::map is faster than into std::unordered_map? – midor Dec 01 '14 at 20:45

score 0 · Answer 2 · answered Dec 01 '14 at 20:55

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I think that you can use a priority queue it will holds the elements {1,1,1,1,3,4,5,5,7} and then manipulate the mode from this queue

answered Dec 01 '14 at 20:55

batuhan

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Andreas DM · Answer 3 · 2014-12-01T21:29:13.413

What you probably would want to do is insert the numbers into a std::vector, use std::sort
(in <algorithm>) on it, and loop through it so see which number occurs the most times.

To give you an idea, you may use std::vector<int>::iterator while looping (use auto instead) to point to the beginning + 1 of the vector, then check if the value to which the iterator points is equals to
iterator - 1. If the current value is higher than max value then store it, along with an iterator to that object.

Hope that helps you on the way.

Finding the mode of n numbers

3 Answers3