【LEETCODE】34、119题，Pascal's Triangle II

package y2019.Algorithm.array;

import java.util.ArrayList;
import java.util.List;

/**
 * @ProjectName: cutter-point
 * @Package: y2019.Algorithm.array
 * @ClassName: GetRow
 * @Author: xiaof
 * @Description: 119. Pascal's Triangle II
 * Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal's triangle.
 * Note that the row index starts from 0.
 * <p>
 * Input: 3
 * Output: [1,3,3,1]
 * <p>
 * 这里和之前的类似，就是获取这个塔的第几行，那么我们每次字需要存上一行，就可以求出下一行数据了
 * a[i,j] = a[i - 1][j-1] + a[i - 1][j]
 * @Date: 2019/7/2 9:13
 * @Version: 1.0
 */
public class GetRow {

    public List<Integer> solution(int rowIndex) {

        List<Integer> preRow = new ArrayList();
        preRow.add(1); //第一行
        List<Integer> curRow = new ArrayList();
        if (rowIndex == 0) {
            return preRow;
        }

        //如果不是第一行
        curRow.add(1);
        for (int i = 1; i <= rowIndex; ++i) {
            //从第二行开始
            curRow = new ArrayList<>();
            for(int j = 0; j < i + 1; ++j) {
                if(j == 0 || j == i) {
                    curRow.add(1);
                } else {
                    curRow.add(preRow.get(j - 1) + preRow.get(j));
                }
            }
            preRow = curRow;
        }

        return curRow;
    }

    public static void main(String args[]) {
        GetRow getRow = new GetRow();
        System.out.println(getRow.solution(0));
    }
}