findNthMin.ts

function findNthMin(nums: number[], nth: number): number | null {
  const total = nums.length;
  if (total === 0 || total < nth || nth <= 0) {
    return null;
  }
  let result = null;
  const sortedNum = sortNum(nums);
  for (let index = 0; index < sortedNum.length; index += 1) {
    const num = sortedNum[index];
    if (index + 1 === nth) {
      result = num;
      index = sortedNum.length;
      break;
    }
  }
  return result;
}

enum sortMode {
  asc = "asc",
  desc = "desc",
}

function sortNum(nums: number[], mode: sortMode = sortMode.asc) {
  if (nums.length <= 1) return nums;
  if (nums.length === 2) {
    if (mode === sortMode.asc) {
      return nums[0] > nums[1] ? [nums[1], nums[0]] : [nums[0], nums[1]];
    }
    return nums[0] > nums[1] ? [nums[0], nums[1]] : [nums[1], nums[0]];
  }

  const middlePos = Math.floor(nums.length / 2);
  const middleNum = nums[middlePos];
  const tempLeft: number[] = [];
  const tempRight: number[] = [];
  nums.forEach((num, index) => {
    if (index !== middlePos) {
      if (num > middleNum) {
        tempRight.push(num);
      } else {
        tempLeft.push(num);
      }
    }
  });

  const _getResultWithMode = () => {
    const resultWithModeMap = {
      [sortMode.asc]: [
        ...sortNum(tempLeft, mode),
        middleNum,
        ...sortNum(tempRight, mode),
      ],
      [sortMode.desc]: [
        ...sortNum(tempRight, mode),
        middleNum,
        ...sortNum(tempLeft, mode),
      ],
    };

    return resultWithModeMap[mode];
  };

  return _getResultWithMode();
}