/**
 * arr 排序后的数据
 * n   几个数
 * start 开始坐标
 * target 总和
 */
function nSum(arr, n, start, target) {
  if (arr.length < 2) return arr;

  if (n < 2) return;

  const result = [];

  let len = arr.length;

  if (n === 2) {
    let left = start;
    let right = len - 1;
    while (left < right) {
      const l = arr[left];
      const r = arr[right];
      const sum = l + r;
      if (sum < target) {
        // 去重
        while (left < right && arr[left] === l) left++;
      } else if (sum > target) {
        // 去重
        while (left < right && arr[right] === r) right--;
      } else {
        result.push([l, r]);
        // 去重
        while (left < right && arr[left] === l) left++;
        while (left < right && arr[right] === r) right--;
      }
    }
  } else {
    for (let i = start; i < len; ) {
      let cur = arr[i];
      const child = nSum(arr, n - 1, i + 1, target - cur);
      if (child.length) {
        for (let ch of child) {
          result.push([cur, ...ch]);
        }
      }
      // 去重
      while (i < len && arr[i] === cur) {
        i++;
      }
    }
  }

  return result;
}

let arr = [1, 2, 3, 4, 5, 6, 2, 6, 7, 8, 7, 3, 53, 123];

function threeSum(arr, target) {
  arr.sort((a, b) => a - b);
  return nSum(arr, 3, 0, target);
}

console.log(threeSum(arr, 14));
//  [[1,5,8],[1,6,7],[2,4,8],[2,5,7],[2,6,6],[3,3,8],[3,4,7],[3,5,6]]