leetcode 118

118. Pascal's Triangle

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]
]

输出Pascal三角形的前n行；每次利用前面已经生成的行来生成下一行。

代码如下：

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> pascal;
        vector<int> ss;
        if(numRows == 0)
        {
            return pascal;
        }
        if(numRows == 1)
        {
            ss.push_back(1);
            pascal.push_back(ss);
            return pascal;
        }
        pascal.push_back({1});
        for(int i = 1; i <numRows; i++)
        {
            for(int j = 0; j <= i; j++)
            {
                if(j == 0 || j == i)
                {
                    ss.push_back(1);
                    continue;
                }
                int n = pascal[i-1][j-1] + pascal[i-1][j];
                ss.push_back(n);
            }
            pascal.push_back(ss);
            ss.clear();
        }
        return pascal;
    }
};