見習村06 - Character with longest consecutive repetition

06 - Character with longest consecutive repetition

Don’t say so much, just coding…

Instruction

For a given string s find the character c (or C) with longest consecutive repetition and return:

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[c, l]

where l (or L) is the length of the repetition. If there are two or more characters with the same l return the first in order of appearance.

For empty string return:

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["", 0]

Ruby

Init

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def longest_repetition chars
  # "Implement me!"
end

Sample Testing

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describe "Solution" do
  it "should work for example tests" do
    Test.assert_equals(longest_repetition("aaaabb"), ['a', 4])
    Test.assert_equals(longest_repetition("bbbaaabaaaa"), ['a', 4])
    Test.assert_equals(longest_repetition("cbdeuuu900"), ['u', 3])
    Test.assert_equals(longest_repetition("abbbbb"), ['b', 5])
    Test.assert_equals(longest_repetition("aabb"), ['a', 2])
    Test.assert_equals(longest_repetition("ba"), ['b', 1])
    Test.assert_equals(longest_repetition(""), ['', 0])
    Test.assert_equals(longest_repetition("aaabbcccddd"), ['a', 3])
  end
end

Javascript

Init

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function longestRepetition(s) {
  // return ["", 0];
}

Sample Testing

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Test.describe("Longest repetition", ()=>{
  Test.it("Example tests", function(){
    Test.assertDeepEquals( longestRepetition("aaaabb"),      ["a",4] );
    Test.assertDeepEquals( longestRepetition("bbbaaabaaaa"), ["a",4] );
    Test.assertDeepEquals( longestRepetition("cbdeuuu900"),  ["u",3] );
    Test.assertDeepEquals( longestRepetition("abbbbb"),      ["b",5] );
    Test.assertDeepEquals( longestRepetition("aabb"),        ["a",2] );
    Test.assertDeepEquals( longestRepetition(""),            ["",0] );
    Test.assertDeepEquals( longestRepetition("ba"),          ["b",1] );
  });
});

Thinking

想法(1): 與 見習村02 - Unique In Order 有點類似，都可以先將輸入的值分群
想法(2): 分群後的陣列，可以再來排序由大到小
想法(3): 排序完成後再來判斷如果傳進來的值是空的要另外回傳 ["", 0]

https://ithelp.ithome.com.tw/upload/images/20200921/20120826gqBHgls5v7.jpg
圖片來源：Unsplash Dayne Topkin

Hint & Reference

Solution

Ruby

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# Solution 1
def longest_repetition chars
  char = chars.gsub(/(.)\1*/).max_by(&:size)
  if char.nil? 
    ['', 0] 
  else 
    [char.split('').first, char.split('').count]
  end
end

# Solution 2
def longest_repetition chars
  char = chars.gsub(/(.)\1*/).max_by(&:size)
  char.nil? ? ['', 0] : [char.split('').first, char.split('').count]
end

# Solution 3
def longest_repetition chars
  return ['', 0] if chars.empty?
  
  char = chars.gsub(/(.)\1*/).max_by(&:size).split('')
  [char.first, char.count]
end

# Solution 4
def longest_repetition chars
  return ["", 0] if chars.empty?
  
  chars.chars.chunk(&:itself)
             .map{ |char, chars| [char, chars.size] }
             .max_by { |char, size| size }     
end

Javascript

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// Solution 1
function longestRepetition(s) {
  let string = s.split("");
  let result = ["", 0];

  for(let i = 0; i < string.length; i++){
    let repetitions = 1;
    while(string[i] == string[i+repetitions]){
      repetitions++;
    }
    if(repetitions > result[1]){
      result = [string[i],repetitions]
    }
  }
  return result;
}