118. Pascal’s Triangle
题意
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]
]
分析
每一层的第i个数等于上一层第i-1个数与第i个数之和
代码
class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<vector<int> > res;
if(numRows == 0)
return res;
vector<int> cur(1,1);
res.push_back(cur);
vector<int> pre = cur;
for(int i = 2; i <= numRows; i ++)
{
pre.push_back(0);
cur = pre;
for(int j = 1; j < i; j ++)
{
cur[j] = pre[j] + pre[j-1];
}
res.push_back(cur);
pre = cur;
}
return res;
}
};
