求给定数组 arr, 求 和为 num 的组合

group.ts

function sum(arr: number[]) {
  return arr.reduce((r, n) => r + n, 0);
}

function group(arr: number[], num: number) {
  const result = [];

  (function loop(unselectedList = [], selectedList = []) {
    if (unselectedList.length === 0) {
      return;
    }

    unselectedList.forEach((_, i) => {
      const newSelectedList = selectedList.concat(unselectedList[i]);
      const valueOfSum = sum(newSelectedList);

      if (valueOfSum >= num) {
        if (valueOfSum === num) {
          result.push(newSelectedList);
        }
        return;
      }

      const newUnselectedList = unselectedList.filter((_, j) => j > i);
      loop(newUnselectedList, newSelectedList);
    });
  })(arr);

  return result;
}

group([1, 2, 3, 4], 3) // [[1,2], [3]]