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> |
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!
Ready to dive in? Explore our Free Demo Content and join our DSA course, trusted by over 100,000 neveropen!