360. Sort Transformed Array

Given a sorted array of integers nums and integer values a, b and c. Apply a function of the form f(x) = ax2 + bx + c to each element x in the array.

The returned array must be in sorted order.

Expected time complexity: O(n)

Example:

nums = [-4, -2, 2, 4], a = 1, b = 3, c = 5,

Result: [3, 9, 15, 33]

nums = [-4, -2, 2, 4], a = -1, b = 3, c = 5

Result: [-23, -5, 1, 7]

public class Solution {
    public int[] sortTransformedArray(int[] nums, int a, int b, int c) {
        if(nums == null || nums.length == 0) return nums;
        if(nums.length == 1){
            nums[0] = eval(nums[0],a,b,c);
            return nums;
        }

        int l = 0;
        int r = nums.length -1;
        int[] res = new int[nums.length];
        int k = 0;
        while(l <= r){ // need to equal to get the final number.
            int v1 = eval(nums[l], a, b, c);
            int v2 = eval(nums[r], a, b, c);

            if(a > 0){
                res[k++] = v1 > v2 ? v1 : v2;
                if(v1 > v2)  l++;
                else r--;
            }else{
                res[k++] = v1 > v2 ? v2 : v1;
                if(v1 > v2 ) r--;
                else l++;
            }
        }

        if(a > 0){
            int left = 0;
            int right = res.length -1;
            while(left < right){
                int tmp = res[left];
                res[left] = res[right];
                res[right] = tmp;
                left++;
                right--;
            }
        }

        return res;
    }

    private int eval(int n, int a, int b, int c){
        return a*n*n + b*n + c;
    }
}

public class Solution {
    public int[] sortTransformedArray(int[] nums, int a, int b, int c) {
        if(nums == null || nums.length <=1) return nums;

        int[] res = new int[nums.length];
        if(a > 0){
            int k = res.length-1;
            int l = 0, r = k;
            while(k >=0){
                int tl = getT(nums[l],a,b,c);
                int tr = getT(nums[r],a,b,c);

                if(tl > tr){
                    res[k] = tl;
                    l++;
                }else{
                    res[k] = tr;
                    r--;
                }
                k--;
            }
        }else if(a < 0){
            int k = 0;
            int l = 0, r = res.length-1;
            while(k < nums.length){
                int tl = getT(nums[l],a,b,c);
                int tr = getT(nums[r],a,b,c);

                if(tl < tr){
                    res[k] = tl;
                    l++;
                }else{
                    res[k] = tr;
                    r--;
                }
                k++;
            }
        }else{
            for(int i= 0; i< res.length;i++){
                res[i] = getT(nums[i], 0,b,c);
            }
            if(b<0){
                int l =0, r = res.length-1;
                while(l < r){
                    int tmp = res[l];
                    res[l] = res[r];
                    res[r] = tmp;
                    l++;
                    r--;
                }
            }
        }

        return res;
    }

    int getT(int x, int a, int b, int c){
        return a*x*x + b*x + c;
    }
}