47 lines
919 B
Ruby
47 lines
919 B
Ruby
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#Given a sorted array arr[] and a number x, write a function that counts the occurrences of x in arr[]
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#Algorithm: Binary Search
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#Time-complexity:O(logn),Auxiliary space:O(1)
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def count_occurences(a,key)
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len=a.length
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#observe boundary conditions
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i=first(a,-1,len-1,key)
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return i if i==-1 # return -1 if key not present in array
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j=last(a,0,len,key)
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return j-i+1,j,i
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end
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def first(a,lo,hi,key)
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#loop to find first occurence
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while hi-lo>1
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mid=lo+(hi-lo)/2
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if a[mid]>=key
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hi=mid
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else
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lo=mid
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end
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end
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if a[hi]==key
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return hi
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else
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return -1
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end
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end
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def last(a,lo,hi,key)
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#loop to find last occurence
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while hi-lo>1
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mid=lo+(hi-lo)/2
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if a[mid]<=key
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lo=mid
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else
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hi=mid
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end
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end
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return lo
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end
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count_occurences([1, 1, 2, 2, 2, 2, 3,3],1)
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