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]
]
solution：
ackage cn.magicdu; import java.util.ArrayList;
import java.util.List; public class _118_Pascal_Triangle { public List<List<Integer>> generate(int numRows) {
if (numRows < 0) {
return null;
}
List<List<Integer>> l1 = new ArrayList<>();
if (numRows >= 1) {
List<Integer> list = new ArrayList<>();
list.add(1);
l1.add(list);
}
if (numRows >= 2) {
List<Integer> list = new ArrayList<>();
list.add(1);
list.add(1);
l1.add(list);
}
if (numRows >= 3) {
for (int i = 3; i <= numRows; i++) {
List<Integer> list = new ArrayList<>();
List<Integer> prev = l1.get(i - 2);
list.add(1);
for (int j = 2; j <= i - 1; j++) {
list.add(prev.get(j - 2) + prev.get(j - 1));
}
list.add(1);
l1.add(list);
} } return l1;
} }