给定一个非负整数 numRows,生成杨辉三角的前 numRows 行。
在杨辉三角中,每个数是它左上方和右上方的数的和。
示例:
输入: 5 输出: [ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]
class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<vector<int>> res;
vector<int> prev;
for (int i = 1; i <= numRows; i++)
{
vector<int> now;
now.push_back(1);
for (int j = 1; j < i-1; j++)
{
int preVal = prev[j-1];
int nowVal = prev[j];
now.push_back(preVal + nowVal);
}
if(i>1)
now.push_back(1);
res.push_back(now);
prev = now;
}
return res;
}
};