calculate sorted y of function y = ax^2 + bx + c given sorted x array

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给定一个一元二次方程式y = ax^2 + bx + c, 一个sorted array X, 将X中所有元素代入方程中，返回sorted的Y

solution: 看a< or > 0,，搞出两边的y们，然后merge

public class Ax2 {    public static void main(String[] args) {    }    // x is sorted array    private static ArrayList<Integer> sorted(int a, int b, int c, int[] x) {        ArrayList<Integer> result = new ArrayList<Integer>();        if (a == 0) {            return result;        }        // the tredence is decresing first then increasing         if (a > 0) {            ArrayList<Integer> list1 = new ArrayList<Integer>();            list1.add(getFun(a, b, c, x[0]));            int i;            for (i = 1; i < x.length; i++) {                int y = getFun(a, b, c, x[i]);                if (y > list1.get(i - 1)) {                    break;                }                list1.add(y);            }            //now the i is the index of first element is larger than previous             ArrayList<Integer> list2 = new ArrayList<Integer>();            for (; i < x.length; i++) {                int y = getFun(a, b, c, x[i]);                list2.add(y);            }            //merge two arraylist            result = mergeList(list1, list2);        } else { //increasing first then decreasing            ArrayList<Integer> list1 = new ArrayList<Integer>();            list1.add(getFun(a, b, c, x[0]));            int i;            for (i = 1; i < x.length; i++) {                int y = getFun(a, b, c, x[i]);                if (y < list1.get(i - 1)) {                    break;                }                list1.add(y);            }            //now the i is the index of first element is larger than previous             ArrayList<Integer> list2 = new ArrayList<Integer>();            for (; i < x.length; i++) {                int y = getFun(a, b, c, x[i]);                list2.add(y);            }            //merge two arraylist            result = mergeList(list1, list2);        }        return result;    }    private static int getFun(int a, int b, int c, int num) {        return (int) (a * Math.pow(num, 2) + b * num + c);    }    private static ArrayList<Integer> mergeList(ArrayList<Integer> list1, ArrayList<Integer> list2) {        ArrayList<Integer> result = new ArrayList<Integer>();        if (list1 == null && list2 != null) {            return list2;        } else if (list1 != null && list2 == null) {            return list1;        }        int i = 0;        int j = 0;        while (i < list1.size() && j < list2.size()) {            if (list1.get(i) < list2.get(j)) {                result.add(list1.get(i));                i++;            } else {                result.add(list2.get(j));                j++;            }        }        if (i != list1.size()) {            for (; i < list1.size(); i++) {                result.add(list1.get(i));            }        }        if (j != list2.size()) {            for (; j < list2.size(); j++) {                result.add(list2.get(j));            }        }        return result;    }

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