~~~ public class Solution { public List<List<Integer>> generate(int numRows) { List<List<Integer>> result = new ArrayList<List<Integer>>(); if(numRows == 0) return result; ArrayList<Integer> first = new ArrayList<Integer>(); first.add(1); result.add(first); for(int n = 2; n <= numRows; n++){ ArrayList<Integer> thisRow = new ArrayList<Integer>(); //the first element of a new row is one thisRow.add(1); //the middle elements are generated by the values of the previous rows //A(n+1)[i] = A(n)[i - 1] + A(n)[i] List<Integer> previousRow = result.get(n- 2); for(int i = 1; i < n - 1; i++){ thisRow.add(previousRow.get(i - 1) + previousRow.get(i)); } //the last element of a new row is also one thisRow.add(1); result.add(thisRow); } return result; } } ~~~