Given a non-negative integer numRows, generate the first numRows of Pascal’s triangle.
In Pascal’s triangle, each number is the sum of the two numbers directly above it.
Example:
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| Input: 5
Output:
[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]
|
暴力算法
直接构造即可 复杂度O(n^2)
注意numRows = 0, 1, 2的特殊情况
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| class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<vector<int>> vvc;
if(numRows == 0) return vvc;
vvc.push_back(vector<int>({1}));
if(numRows == 1) return vvc;
vvc.push_back(vector<int>({1,1}));
if(numRows == 2) return vvc;
assert(numRows > 2);
for(int j = 3; j <= numRows; ++j)
{
vector<int> tmp;
tmp.push_back(1);
for(int i = 0; i < j - 2; ++i)
{
int a = vvc.back()[i] + vvc.back()[i + 1];
tmp.push_back(a);
}
tmp.push_back(1);
vvc.push_back(tmp);
}
return vvc;
}
};
|