题目地址

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

题目描述

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]
]

思路

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。

关键点解析

代码

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

本文参考自：
https://github.com/grandyang/leetcode/ &
https://github.com/azl397985856/leetcode