119. Pascal's Triangle II java solutions

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,
Return [1,3,3,1].

Note:
Could you optimize your algorithm to use only O(k) extra space?

public class Solution {
    public List<Integer> getRow(int rowIndex) {
        Integer[] num = new Integer[rowIndex+1];
        num[0] = 1;
        for(int i = 1; i < num.length; i++){
            num[i] = (int)((long)num[i-1]*(rowIndex-i+1)/i);//不加强制转换，乘积大于Integer.MAX_VALUE有溢出
        }
        return Arrays.asList(num);
    }
}

public class Solution {
    public List<Integer> getRow(int rowIndex) {
        List<Integer> list = new ArrayList<Integer>();
        list.add(1);
        for(int i = 1; i < rowIndex + 1; i++){
            list.add((int)((long)list.get(i-1)*(rowIndex-i+1)/i));
        }
        return list;
    }
}

根据数学公式：

[C(k,0), C(k,1), ..., C(k, k-1), C(k, k)]

C[k,i] = C[k,i-1]*(k-i+1)/i