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55 lines
1.2 KiB
Ruby
55 lines
1.2 KiB
Ruby
#Given an Bitonic Array(array of integers which is initially increasing and then decreasing),
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#find the maximum value in the array
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#Time-complexity: O(logn),Auxiliary-space:O(1)
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#Algorithm: Binary-search
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=begin
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#caveat:This method works only for distinct numbers,
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coz in case of too many duplicates cause it not possible to decide by constant comparisons at mid, which subarray to choose
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#it will not work for an array like {0, 1, 1, 2, 2, 2, 2, 2, 3, 4, 4, 5, 3, 3, 2, 2, 1, 1} .
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=end
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# Recursive
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def maximum(a,lo,hi)
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if lo==hi
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return a[lo]
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end
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if hi==lo+1
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if arr[lo]<arr[hi]
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return a[hi]
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else
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return a[lo]
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end
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end
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mid=lo+(hi-lo)/2
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return a[mid] if (a[mid]>a[mid+1] && a[mid]>a[mid-1])
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if (a[mid]>a[mid+1] && a[mid]<a[mid-1])
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return maximum(a,lo,mid-1)
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else
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return maximum(a,mid+1,hi)
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end
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end
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maximum([1,2,3,4,2,1],0,3) #=> 4
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#Iterative
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def maximum(a)
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lo=0
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hi=a.length-1
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while hi-lo>1
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mid=lo+(hi-lo)/2
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if a[mid]>a[mid-1]
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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 [a[lo],a[hi]].max
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end
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maximum([1,2,3,4,2,1]) #=> 4 |