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]

]

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