52 lines
1.4 KiB
Ruby
52 lines
1.4 KiB
Ruby
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# Problem:
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=begin
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Given an array of size N ,taht has elements in range 1 to N ,all elements in the arrayb are unique,
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Find the missing number.
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e.g.
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array = [1,5,2,4,6]
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answer = 3
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=end
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#Approach 1 - Find the sum of all elements of array and substract it from sum of the range , the difference will be missing number.
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# Time-complexity = O(n)
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#Caveats: If the numbers are very large the sum can lead to integer overflow.
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def find_missing_number(a)
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n = a.length+1
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range_sum = (n * (n+1))/2 # Sum of numbers from 1 to n is (n* n+1 )/2
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arr_sum = 0
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for x in a
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arr_sum+=x
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end
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return missing_element = range_sum - arr_sum
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end
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#Approach 2 (No integer overflow)- Take bitwise XOR of all elements of the array with the numbers in given range,
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#As( a XOR a == 0 ) all numbers present in array will xor out and become zero except the missing number.
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# Time-complexity = O(n)
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def find_missing_number(a)
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n = a.length+1
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missing_element = 0
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(1..n).each {|num| missing_element^= num}
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for x in a
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missing_element^=x
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end
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return missing_element
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end
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#Ruby magic
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#One line code but it uses O(n) auxiliary-space, it returns an array containing only the missing_element
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# Array1-Array2 in ruby returns an array containing all the elements that are in Array1 but not in Array2
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def find_missing_number(a)
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n = a.length+1
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range = Array (1..n)
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missing_element = range-a
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end
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