[Leetcode] Pascal's Triangle (Java)

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]]

生成杨辉三角

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