ソートとツーポインタで目標にいちばん近い 3 つの和を求める

def three_sum_closest(
    nums, target
):
    a = sorted(nums)
    n = len(a)
    best = a[0] + a[1] + a[2]
    gap = abs(best - target)
    for i in range(n - 2):
        x = a[i]
        j = i + 1
        k = n - 1
        while j < k:
            s = x + a[j] + a[k]
            if s == target:
                return s
            d = abs(s - target)
            if d < gap:
                best = s
                gap = d
            if s < target:
                j += 1
            else:
                k -= 1
    return best

function threeSumClosest(
  nums, target
) {
  const a = [...nums].sort(
    (p, q) => p - q
  );
  const n = a.length;
  let best = a[0] + a[1] + a[2];
  let gap = Math.abs(
    best - target
  );
  const m = n - 2;
  for (let i = 0; i < m; i++) {
    const x = a[i];
    let j = i + 1;
    let k = n - 1;
    while (j < k) {
      const s = x + a[j] + a[k];
      if (s === target) {
        return s;
      }
      const d = Math.abs(
        s - target
      );
      if (d < gap) {
        best = s;
        gap = d;
      }
      if (s < target) {
        j++;
      } else {
        k--;
      }
    }
  }
  return best;
}

import "sort"

func threeSumClosest(
	nums []int, target int,
) int {
	a := append([]int{}, nums...)
	sort.Ints(a)
	n := len(a)
	best := a[0] + a[1] + a[2]
	gap := absInt(best - target)
	for i := 0; i+2 < n; i++ {
		x := a[i]
		j, k := i+1, n-1
		for j < k {
			s := x + a[j] + a[k]
			if s == target {
				return s
			}
			d := absInt(s - target)
			if d < gap {
				best, gap = s, d
			}
			if s < target {
				j++
			} else {
				k--
			}
		}
	}
	return best
}

func absInt(x int) int {
	if x < 0 {
		return -x
	}
	return x
}