Question

find a pair of elements from an array whose sum equals a given number in c in o(n)

Answer 1

Given an array of integers, and a number ‘sum’, find the number of pairs of integers in the array whose sum is equal to ‘sum’.

Examples: Input : arr[] = {1, 5, 7, -1}, sum = 6 Output : 2 Pairs with sum 6 are (1, 5) and (7, -1) Input : arr[] = {1, 5, 7, -1, 5}, sum = 6 Output : 3 Pairs with sum 6 are (1, 5), (7, -1) & (1, 5) Input : arr[] = {1, 1, 1, 1}, sum = 2 Output : 6 There are 3! pairs with sum 2. Input : arr[] = {10, 12, 10, 15, -1, 7, 6, 5, 4, 2, 1, 1, 1}, sum = 11 Output : 9