[LeetCode] Pascal's Triangle 杨辉三角

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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