2021-01-20

62.不同路径

class Solution(object):
    def uniquePaths(self, m, n):
        dp = [[0 for _ in range(n)] for _ in range(m)]
        
        dp[0][0] = 0
        for i in range(m):
            dp[i][0] = 1
        for j in range(n):
            dp[0][j] = 1
        
        for i in range(1, m):
            for j in range(1, n):
                dp[i][j] = dp[i-1][j] + dp[i][j-1]
        return dp[-1][-1]

70.爬楼梯

class Solution:
    def climbStairs(self, n: int) -> int:
        f=lambda x:f(x-1)*x if x>=2 else 1
        i=r=1
        while n>i:
            n-=1
            r+=f(n)/(f(i)*f(n-i))
            i+=1
        return int(r)

78.子集

class Solution(object):
    def subsets(self, nums):
        res = [[]]
        for i in range(len(nums)-1, -1, -1):
            for subres in res[:]: res.append(subres+[nums[i]])
    
        return res