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]
]

思路：杨辉三角 很简单的逻辑判断 但看了某大神的代码 还是有的不小的差距 在时间上和简洁度上 
C++代码：

class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<vector<int>> res;
vector<int> btemp;
if(numRows==0)
return res;
btemp.push_back(1);
res.push_back(btemp);
if(numRows==1){

return res;
}
for(int i=2;i<=numRows;i++){
vector<int> temp;
for(int j=0;j<i;j++){
if(j==0||j==i-1)
temp.push_back(1);
else
temp.push_back(btemp[j-1]+btemp[j]);
}
btemp.clear();
btemp = temp;
res.push_back(temp);
}
return res;
}
};大神的代码：简单明了 得多学习下代码的简洁了
class Solution {
public:
vector<vector<int> > generate(int numRows) {
vector<vector<int>> r(numRows);

for (int i = 0; i < numRows; i++) {
r[i].resize(i + 1);
r[i][0] = r[i][i] = 1;

for (int j = 1; j < i; j++)
r[i][j] = r[i - 1][j - 1] + r[i - 1][j];
}

return r;
}
};