Pascal's Triangle II | Leetcode

Given an index k, return the k^th 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?

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Solution: Edit the same array in-place. For index i, since we are going to use indexes i-1 and i to update index i, we need to save the pre-modified value at index i to calculate the next value.

public class Solution {
    public List<Integer> getRow(int rowIndex) {
        List<Integer> list = new ArrayList<>();
        list.add(1);
        for (int i = 0; i < rowIndex; i++) {
            int last = list.get(0);
            for (int j = 1; j < list.size(); j++) {
                int temp = list.get(j);
                list.set(j, last + list.get(j));
                last = temp;
            }
            list.add(1);
        }
        return list;
    }
}