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
Expected time complexity O(n)
Naive Solution – A simple solution is to traverse each element and check if there’s another number in the array which can be added to it to give sum.
Javascript
<script> // Javascript implementation of simple method to find count of // pairs with given sum. // Returns number of pairs in arr[0..n-1] with sum equal // to 'sum' function getPairsCount(arr, n, sum) { let count = 0; // Initialize result // Consider all possible pairs and check their sums for (let i = 0; i < n; i++) for (let j = i + 1; j < n; j++) if (arr[i] + arr[j] == sum) count++; return count; } // Driver function to test the above function let arr = [ 1, 5, 7, -1, 5 ]; let n = arr.length; let sum = 6; document.write("Count of pairs is " + getPairsCount(arr, n, sum)); // This code is contributed by Mayank Tyagi </script> |
Output
Count of pairs is 3
Time Complexity: O(n2)
Auxiliary Space: O(1)
Please refer complete article on Count pairs with given sum for more details!
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