CODE 15. Pascal's Triangle

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/09/16/2013-09-16-CODE 15 Pascal's Triangle/

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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]
]
My Code:

public ArrayList<ArrayList<Integer>> generate(int numRows) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (numRows <= 0) {
		return new ArrayList<ArrayList<Integer>>();
	}
	ArrayList<ArrayList<Integer>> pascalsTriangle = new ArrayList<ArrayList<Integer>>();
	ArrayList<Integer> layer = new ArrayList<Integer>();
	layer.add(1);
	pascalsTriangle.add(layer);
	for (int i = 1; i < numRows; i++) {
		ArrayList<Integer> layeri = new ArrayList<Integer>();
		ArrayList<Integer> layerj = pascalsTriangle.get(i - 1);
		layeri.add(1);
		for (int j = 1; j <= i; j++) {
			if (j == i) {
				layeri.add(1);
			} else {
				layeri.add(layerj.get(j) + layerj.get(j - 1));
			}
		}
		pascalsTriangle.add(layeri);
	}
	return pascalsTriangle;
}