CODE EXAMPLE FOR PYTHON

Counting Pairs in an Array, resulting in a given sum

<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 , k) {
        var m = new Map();
        var count = 0;
        for (var i = 0; i < n; i++) {
            if (m.has(k - arr[i])) {
                count += m.get(k - arr[i]);
            }
            if (m.has(arr[i])) {
                m.set(arr[i], m.get(arr[i]) + 1);
            } else {
                m.set(arr[i], 1);
            }
        }
        return count;
    }
 
    // Driver function to test the above function
        var arr = [ 1, 5, 7, -1, 5 ];
        var n = arr.length;
        var sum = 6;
        document.write("Count of pairs is " + getPairsCount(arr, n, sum));
 
// This code is contributed by umadevi9616
</script>