leetcode: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]
]
杨辉三角，只不过使用容器的形式表现出来。

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