Leetcode 细节实现 Pascal's Triangle

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Pascal's Triangle

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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]
]

题意：给定数字numRows，返回杨辉三角的前numRows行

思路：按杨辉三角的定义生成即可
复杂度：时间O(n^2)，空间O(n^2)

class Solution {
public:
vector<vector<int> > generate(int numRows){
vector<vector<int> > triangle;
if(numRows == 0) return triangle;
vector<int> row1; row1.push_back(1);
triangle.push_back(row1);
for(int i = 1; i < numRows; i++){
vector<int> row;
row.push_back(1);
for(int j = 0; j < i - 1; j++){
row.push_back(triangle[i - 1][j] + triangle[i - 1][j + 1]);
}
row.push_back(1);
triangle.push_back(row);
}
return triangle;
}
};