pascals-triangle-ii

/**
 * 给出一个索引k，返回杨辉三角的第k行
 * 例如，k=3，
 * 返回[1,3,3,1].
 * 备注：
 * 你能将你的算法优化到只使用O(k)的额外空间吗?
 *
 * Given an index k, return the k th row of the Pascal's triangle.
 * For example, given k = 3,
 * Return[1,3,3,1].
 * Note:
 * Could you optimize your algorithm to use only O(k) extra space?
 */

import java.util.ArrayList;

/**
 * 给出一个索引k，返回杨辉三角的第k行
 * 例如，k=3，
 * 返回[1,3,3,1].
 * 备注：
 * 你能将你的算法优化到只使用O(k)的额外空间吗?
 *
 * Given an index k, return the k th row of the Pascal's triangle.
 * For example, given k = 3,
 * Return[1,3,3,1].
 * Note:
 * Could you optimize your algorithm to use only O(k) extra space?
 */

public class Main54 {
    public static void main(String[] args) {
        System.out.println(Main54.getRow(3));
    }

    public static ArrayList<Integer> getRow(int rowIndex) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        ArrayList<Integer> array = new ArrayList<>();

        if (rowIndex == 0) {
            return array;
        }

        for (int i=0;i<rowIndex;i++) {
            ArrayList<Integer> newArray = new ArrayList<>();
            if (i > 1) {
                array = list.get(i-1);
            }

            for (int j=0;j<=i;j++) {
                if (j==0 || i==j) {
                    newArray.add(1);
                }else{
                    newArray.add(array.get(j-1)+array.get(j));

                }
            }
            list.add(newArray);
        }
        return list.get(list.size()-1);
    }
}