Pascal's Triangle II

问题来源：https://leetcode.com/problems/pascals-triangle-ii/

import java.util.ArrayList;import java.util.List;/** *  * <p> * ClassName PascalIsTriangleII * </p> * <p> * Description Given an index k, return the kth 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? * </p> *  * @author TKPad [e-mail] *         <p> *         Date 2015年3月27日 下午2:15:35 *         </p> * @version V1.0.0 * */public class PascalIsTriangleII {    public List<Integer> getRow(int rowIndex) {        return generate(rowIndex + 1);    }    public List<Integer> generate(int numRows) {        if (numRows <= 0) {            return new ArrayList<Integer>();        }        List<Integer> temp = new ArrayList<Integer>();// 使用temp作为一个迭代器，来不断产生新的List        temp.add(1);        for (int i = 1; i < numRows; i++) {            List<Integer> generateList = generateList(temp);            temp = generateList;        }        return temp;    }    public List<Integer> generateList(List<Integer> temp) {        int first = temp.get(0);        ArrayList<Integer> al = new ArrayList<Integer>();        al.add(first);        for (int i = 1; i < temp.size(); i++) {            al.add(first + temp.get(i));            first = temp.get(i);        }        al.add(temp.get(0));        return al;    }    public static void main(String[] args) {        List<Integer> row = new PascalIsTriangleII().getRow(0);        System.out.println(row);    }}