0360. Sort Transformed Array

https://leetcode.com/problems/sort-transformed-array

Description

Given a sorted integer array nums and three integers a, b and c, apply a quadratic function of the form f(x) = ax2 + bx + c to each element nums[i] in the array, and return the array in a sorted order.

Example 1:

**Input:** nums = [-4,-2,2,4], a = 1, b = 3, c = 5
**Output:** [3,9,15,33]

Example 2:

**Input:** nums = [-4,-2,2,4], a = -1, b = 3, c = 5
**Output:** [-23,-5,1,7]

Constraints:

• 1 <= nums.length <= 200

• -100 <= nums[i], a, b, c <= 100

• nums is sorted in ascending order.

Follow up: Could you solve it in O(n) time?

ac

class Solution {
    public int[] sortTransformedArray(int[] nums, int a, int b, int c) {
        // edge cases
        if (nums == null || nums.length == 0) return new int[0];

        int[] res = new int[nums.length];

        // 2 pointers
        int l = 0, r = res.length - 1;
        if (a < 0) {
            int i = l;
            while (l <= r) {
                int left = a * nums[l] * nums[l] + b * nums[l] + c;
                int right = a * nums[r] * nums[r] + b * nums[r] + c;
                if (left < right) {
                    res[i++] = left;
                    l++;
                } else {
                    res[i++] = right;
                    r--;
                }
            }
        } else {
            int i = r;
            while (l <= r) {
                int left = a * nums[l] * nums[l] + b * nums[l] + c;
                int right = a * nums[r] * nums[r] + b * nums[r] + c;
                if (left > right) {
                    res[i--] = left;
                    l++;
                } else {
                    res[i--] = right;
                    r--;
                }
            }
        }

        return res;
    }
}
/*
upward, downward


*/