leetcode——118—— 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]
]

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class Solution {
public:
	vector<vector<int> > generate(int numRows) {
		vector<vector<int> > ret;
		if (numRows == 0)
			return ret;

		vector<int> last(1, 1);
		ret.push_back(last);
		for (int i = 2; i <= numRows; i++)
		{// i_th level
			last.push_back(0);
			vector<int> cur = last;
			for (int j = 1; j < i; j++)
			{
				cur[j] = last[j] + last[j - 1];
			}
			ret.push_back(cur);
			last = cur;
		}
		return ret;
	}
};