Pascal's Triangle

c++

class Solution {public:    vector<vector<int>> generate(int numRows) {        vector<vector<int>> res;        if (numRows <= 0)            return res;        res.push_back(vector<int>(1, 1));        for (int i = 1; i < numRows; ++i) {            vector<int> tmp;            tmp.push_back(1);            for (int j = 0; j < i - 1; ++j) {                tmp.push_back(res[i-1][j] + res[i - 1][j + 1]);            }            tmp.push_back(1);            res.push_back(tmp);        }        return res;    }};

python

class Solution(object):    def generate(self, numRows):        """        :type numRows: int        :rtype: List[List[int]]        """        if numRows <=0:            return []        res = []        a = [1]        res.append(a)        for x in xrange(numRows-1):            a = [sum(i) for i in zip([0] + a, a + [0])]            res.append(a)        return res