46 lines
1.1 KiB
Ruby
46 lines
1.1 KiB
Ruby
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=begin
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#Counting Sort is a linear time sort used when range of keys is already known.
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#Algorithm
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1. Take a count array to store the frequency of each value in given range
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2. change count[i] to count[i]+count[i-1],i.e each element now stores the prefix sum of counts.
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3. take each value from the array and put it at the correct index in output array using count, decrement value of count! (correct index of a[i] will be count[a[i]-1])
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4.Finally copy the values of output array to array.
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# n is the size of array and k is the range of input
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#Time-complexity: O(n+k), Auxiliary-space:O(n+k), Not In-place, Not stable
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=end
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def counting_sort(a=[9,8,7,6],min=0,max=10)
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if min>max
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return "invalid range"
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end
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n=max-min+1
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count=Array.new(n,0)
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len=a.length
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output=Array.new(len)
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for i in 0...len
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count[a[i]-min]+=1
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end
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for i in 1...n
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count[i]+=count[i-1]
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end
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for i in 0...len
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output[count[a[i]-min]-1]=a[i]
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count[a[i]-min]-=1
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end
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for i in 0...len
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a[i]=output[i]
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end
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return a
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end
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counting_sort([9,8,1,2,3,7],-3,10)
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