Question

Given an unsorted array of distinct positive integers A [ 1......n ] in the range between 1 and 10000 and an integer i in the sane range. Here n can be arbitrary large You want to find out whether there are 2 elements of the array that add up to i. Give an algorithm that runs in time (O(n).

Answer 1

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find(A,n,i)
for j =0 to 10000 do
frequency[j]=0
for j=1 to n do
frequency[A[j]]= frequency[A[j]]+1
for j =1 to n do
if i>=A[j] then
if (i-A[j])!=A[j] and frequency[i-A[j]]>0 then
return true
else if (i-A[j])==A[j] and frequency[j-A[j]]>1 then
return true
else
if (A[j]-i)!=A[j] and frequency[A[j]-i]>0 then
return true
else if (A[j]-i)==A[j] and frequency[A[j]-i]>1 then
return true
return false