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]

]

方法一、

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;
}

方法二、

vector<vector<int>> generate(int numRows) {
if(numRows == 0)
{
return vector<vector<int>> ();
}

vector<vector<int>> result;
int i = 0;
int j = 0;
for(i = 0; i < numRows; i++)
{
vector<int> temp;
for(j = 0; j < i+1; j++ )
{
if(i==0 || j==i)
{
temp.push_back(1);
}
else
{
temp.push_back(result[i-1][j-1]+result[i-1][j]);
}
}

result.push_back(temp);
}

return result;
}