Leetcode 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]

抛物线开口朝上，max一定出现在两端，抛物线开口朝下，min一定出现在两端。
用双指针来进行排序。

public class Solution {

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

public int[] sortTransformedArray(int[] nums, int a, int b, int c) {
int index;
if(a > 0){
index = nums.length - 1 ;
} else {
index = 0;
}
int result[] = new int[nums.length];
int i = 0;
int j = nums.length - 1;
if(a > 0){
while(i <= j){
result[index--] = calcu(nums[i],a,b,c) > calcu(nums[j],a,b,c) ? calcu(nums[i++],a,b,c):calcu(nums[j--],a,b,c);
}
}else{
while(i <= j){
result[index++] = calcu(nums[i],a,b,c) < calcu(nums[j],a,b,c) ? calcu(nums[i++],a,b,c):calcu(nums[j--],a,b,c);
}
}
return result;
}
}