1+ # Pair with Target Sum (easy)
2+ # Given an array of sorted numbers and a target sum, find a pair in the array whose sum is equal to the given target.
3+ 4+ # Write a function to return the indices of the two numbers (i.e. the pair) such that they add up to the given target.
5+ 6+ # Input: [1, 2, 3, 4, 6], target=6
7+ # Output: [1, 3]
8+ # Explanation: The numbers at index 1 and 3 add up to 6: 2+4=6
9+ 10+ def pair_with_targetsum (arr , target_sum ):
11+ left , right = 0 , len (arr ) - 1
12+ while (left < right ):
13+ current_sum = arr [left ] + arr [right ]
14+ if current_sum == target_sum :
15+ return [left , right ]
16+ 17+ if target_sum > current_sum :
18+ left += 1 # we need a pair with a bigger sum
19+ else :
20+ right -= 1 # we need a pair with a smaller sum
21+ return [- 1 , - 1 ]
22+ 23+ def pair_with_targetsum2 (arr , target_sum ):
24+ nums = {} # to store numbers and their indices
25+ for i , num in enumerate (arr ):
26+ if target_sum - num in nums :
27+ return [nums [target_sum - num ], i ]
28+ else :
29+ nums [arr [i ]] = i
30+ return [- 1 , - 1 ]
31+ 32+ def main ():
33+ print (pair_with_targetsum ([1 , 2 , 3 , 4 , 6 ], 6 ))
34+ print (pair_with_targetsum ([2 , 5 , 9 , 11 ], 11 ))
35+ print ('---' )
36+ print (pair_with_targetsum2 ([1 , 2 , 3 , 4 , 6 ], 6 ))
37+ print (pair_with_targetsum2 ([2 , 5 , 9 , 11 ], 11 ))
38+ 39+ main ()
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