118. Pascal's Triangle

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

[     [1],    [1,1],   [1,2,1],  [1,3,3,1], [1,4,6,4,1]]

Pascal's Triangle的解释可以参考：https://en.wikipedia.org/wiki/Pascal's_triangle

代码如下：

public class Solution {    public List<List<Integer>> generate(int numRows) {        List<List<Integer>> allrows = new ArrayList<List<Integer>>();        ArrayList<Integer> row = new ArrayList<Integer>();        for (int i = 0; i < numRows; i ++) {            row.add(0, 1);            for (int j = 1; j < row.size() - 1; j ++) {                row.set(j, row.get(j) + row.get(j + 1));            }            allrows.add(new ArrayList<Integer>(row));        }        return allrows;    }}