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 == )
         {
             return pascal;
         }
         if(numRows == )
         {
             ss.push_back();
             pascal.push_back(ss);
             return pascal;
         }
         pascal.push_back({});
         for(int i = ; i <numRows; i++)
         {
             for(int j = ; j <= i; j++)
             {
                 if(j ==  || j == i)
                 {
                     ss.push_back();
                     continue;
                 }
                 int n = pascal[i-][j-] + pascal[i-][j];
                 ss.push_back(n);
             }
             pascal.push_back(ss);
             ss.clear();
         }
         return pascal;
     }
 };