find-ordered-pairs.ts

function findOrderedPairs(arr: number[], sum: number) {
    const result: number [][] = [];
    arr.sort((a ,b) => a - b);

    let low = 0, high = arr.length - 1;

    while (low < high) {
        if (arr[low] + arr[high] < sum) {
            low++;
        } else if (arr[low] + arr[high] > sum) {
            high--;
        } else {
            result.push([arr[low], arr[high]]);
            result.push([arr[high], arr[low]]);

            let runner = low + 1;
            while (runner < high && arr[runner] === arr[low]) {
                result.push([arr[runner], arr[high]]);
                result.push([arr[high], arr[runner]]);
                runner++;
            }
            high--;
        }
    }
    return result;
}

console.log(findOrderedPairs([1, 3, 3, 3], 6));
// output: [ [ 3, 3 ], [ 3, 3 ], [ 3, 3 ], [ 3, 3 ], [ 3, 3 ], [ 3, 3 ] ]