Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example:

Input: 5

Output:

[

     [1],

    [1,1],

   [1,2,1],

  [1,3,3,1],

 [1,4,6,4,1]

]

杨辉三角是二项式系数的一种写法，如果熟悉杨辉三角的五个性质，那么很好生成，可参见我的上一篇博文Pascal's Triangle II。具体生成算是：每一行的首个和结尾一个数字都是1，从第三行开始，中间的每个数字都是上一行的左右两个数字之和。代码如下：

class Solution {

public:

    vector<vector<int>> generate(int numRows) {

        vector<vector<int>> res(numRows, vector<int>());

        for (int i = ; i < numRows; ++i) {

            res[i].resize(i + , );

            for (int j = ; j < i; ++j) {

                res[i][j] = res[i - ][j - ] + res[i - ][j];

            }

        }

        return res;

    }

};

类似题目：

Pascal's Triangle II

参考资料：

https://leetcode.com/problems/pascals-triangle/

https://leetcode.com/problems/pascals-triangle/discuss/38150/My-C%2B%2B-code-0ms

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