八. 递归
递归代码模板：
def recursion(level, param1, param2, ...):
# recursion terminator
if level > MAX_LEVEL:
print_result
return
# process logic in current level
process_data(level, data...)
# drill down
self.recursion(level+1, p1, ...)
# reverse the current level status if needed
reverse_state(level)
118. 杨辉三角
题目：获取杨辉三角的前几行
输入：numRows = 5
输出： [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]
def generate(self, numRows: int) -> List[List[int]]:
if numRows == 0:
return []
if numRows == 1:
return [[1]]
if numRows > 1:
res = self.generate(numRows-1) # 递归
newlist = [1]
for i in range(0, numRows-2):
newlist.append(res[numRows-2][i]+res[numRows-2][i+1])
newlist.append(1)
res.append(newlist)
return res
119. 杨辉三角 II
题目：获取杨辉三角的某一行
输入：rowIndex = 3
输出：[1,3,3,1]
def getRow(self, rowIndex: int) -> List[int]:
if rowIndex == 0:
return [1]
if rowIndex == 1:
return [1, 1]
if rowIndex > 1:
res = self.getRow(rowIndex-1)
newlist = [1]
for i in range(0, rowIndex-1):
newlist.append(res[i]+res[i+1])
newlist.append(1)
return newlist
