[LeetCode] Pascal's Triangle

[LeetCode] 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]
]

public class Solution {
    public List> generate(int numRows) {
    	List> res = new ArrayList<>();
    	if(numRows<=0) return res;
    	List lin = new ArrayList<>();
    	lin.add(1);
    	res.add(lin);
    	if(numRows==1) return res; 
        for(int i=0;i list = new ArrayList<>();
        	List pre = res.get(i);
        	list.add(1);
        	for(int j=0;j


遞歸版本

public class Solution {
	List> res = new ArrayList<>();
    public List> generate(int numRows) {
    	if(numRows<=0) return res;
    	helpGenerate(numRows);
    	return res;
    }
    
    private List helpGenerate(int numRows){
    	if(numRows == 1){
    		List list = new ArrayList<>();
    		list.add(1);
    		res.add(list);
    		return list;
    	}
    	List pre = helpGenerate(numRows-1);
    	List list = new ArrayList<>();
    	list.add(1);
    	for(int i=0;i