https://codereview.stackexchange.com/questions/98448/free-code-camp-pairwise

pairwise.ts

export function pairwise (values: number[], check: number): number {
    const sorted = Array.from(values.entries());

    sorted.sort((a, b) => {
        let res = Math.sign(a[1] - b[1]);
        if (res === 0) {
            res = Math.sign(a[0] - b[0]);
        }

        return res;
    });

    let i = 0;
    let j = sorted.length - 1;
    let total = 0;

    while (i < j) {
        const sum = sorted[i][1] + sorted[j][1];
        if (sum < check) {
            i++;
            continue;
        }
        if (sum > check) {
            j--;
            continue;
        }
        let k = j - 1;
        while (k > i && sorted[k][1] === sorted[j][1]) {
            k--;
        }
        k++;
        total += sorted[i][0] + sorted[k][0];
        i++;
        j = k - 1;
    }

    return total;
}