leetcode 生成杨辉三角形， 118 119 Pascal's Triangle 1，2

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]
]

解决方案：

vector<vector<int>> generate(int numRows) {
vector<vector<int>> res = {};
for (int i = 0; i < numRows; i++) {
res.push_back(vector<int>(i + 1, 1));
for(int j = 1; j < i; j++) {
res[i][j] = (res[i - 1][j] + res[i - 1][j - 1]);
}
}
return res;

}

Pascal's Triangle II
Total Accepted: 46342
Total Submissions: 157260

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,

Return

[1,3,3,1]

.

Note:

Could you optimize your algorithm to use only O(k) extra space?

我的解决方案：

从没一行的倒数第二个算起，往前面逆推：

vector<int> getRow(int rowIndex)
{
vector<int> result(rowIndex + 1, 1);

for(int i = 1; i <= rowIndex; ++i)
{
for(int j = i - 1; j > 0; --j)
{
result[j] = result[j] + result[j - 1];
}
}

return result;
}

递归的解决方案：

vector<int> getRow(int rowIndex) {
vector<int> result;

if (rowIndex == 0) {
result.push_back(1);

return result;
} else {
vector<int> vec = getRow(rowIndex - 1);
result.push_back(1);
for (size_t i = 0; i < vec.size() - 1; i++) {
result.push_back(vec[i] + vec[i+1]);
}
result.push_back(1);
}
}

python 解决方案：

class Solution:
# @param {integer} rowIndex
# @return {integer[]}
def getRow(self, rowIndex):
row = [1]
for i in range(1, rowIndex+1):
row = list(map(lambda x,y: x+y, [0]+row, row + [0]))
return row