Pascal's Triangle II @LeetCode

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?

	package leetcode;
	import java.util.ArrayList;
	/**
	* Solution: Same to Pascal's Triangle I.
	* Use a result to remember the previous line result. Other steps are same to I.
	* At first, I'd like to create a rowIndex + 1 size ArrayList. every time I can use it
	* to store result. But I can't code it out. this is the real O(k) space.
	*
	* Every problem with limited space, we need to consider reuse some space we have.
	* Like Set Matrix Zeros
	*
	* @author jeffwan
	* @date Apr 3, 2014
	*/
	public class PascalTriangleII {
	public ArrayList<Integer> getRow(int rowIndex) {
	ArrayList<Integer> result = new ArrayList<Integer>();
	if (++rowIndex == 0) {
	return result;
	}
	result.add(1);
	for (int i = 1; i < rowIndex; i++) {
	ArrayList<Integer> temp = new ArrayList<Integer>(i + 1);
	for (int j = 0; j < i + 1; j++) {
	temp.add(-1);
	}
	temp.set(0, result.get(0));
	temp.set(i, result.get(i - 1));
	for (int j = 1; j < i; j++) {
	temp.set(j, result.get(j - 1) + result.get(j));
	}
	result = temp;
	}
	return result;
	}
	}

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