Given an integer numRows, return the first numRows of Pascal's triangle.
In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:
Example 1:
Input: numRows = 5
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
Example 2:
Input: numRows = 1
Output: [[1]]
Constraints:
- 1 <= numRows <= 30
class Solution {
public List<List<Integer>> generate(int numRows) {
List<List<Integer>> lists= new ArrayList<>();
if(numRows==0) {
return lists;
}
if(numRows>=1) {
List<Integer> list = new ArrayList<>();
list.add(1);
lists.add(list);
}
if(numRows>=2) {
List<Integer> list = new ArrayList<>();
list.add(1);
list.add(1);
lists.add(list);
}
if(numRows>=3){
for(int i=3;i<=numRows;i++){
List<Integer> list = new ArrayList<>();
list.add(1);
List<Integer> pre = lists.get(i-1-1);
for(int j=1;j<i-1;j++){
list.add(pre.get(j-1)+pre.get(j));
}
list.add(1);
lists.add(list);
}
}
return lists;
}
}