LeetCode 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]
]

Pascal三角的规则是：每一个数等于头上左右两个数之和。

class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<int> v;
vector<vector<int>> res;
if(numRows == 0) return res;
v.push_back(1);
res.push_back(v);
if(numRows == 1) return res;
v.push_back(1);
res.push_back(v);
if(numRows == 2) return res;
v.clear();
int i;
for(i = 3; i <= numRows; i ++){
v.push_back(1);
int j;
for(j = 1; j < i - 1; j ++){
v.push_back(res[i - 2][j - 1] + res[i - 2][j]);
}
v.push_back(1);
res.push_back(v);
v.clear();
}
return res;
}
};