43. 字串相乘

def multiply(self, num1, num2):
        res = 0
        for i in range(1,len(num1)+1):
            for j in range(1, len(num2)+1):
                res += int(num1[-i]) * int(num2[-j]) *10**(i+j-2)
        return str(res)

46… 全排列

class Solution:
    def permute(self, nums: List[int]) -> List[List[
 
int]]:
        res = []
        def backtrack(nums, tmp):
            if not nums:
                res.append(tmp)
                return 
            for i in range(len(nums)):
                backtrack(nums[:i] + nums[i+1:], tmp + [nums[i]])
        backtrack(nums, [])
        return res

53… 最大子序和

class Solution(object):
    def maxSubArray(self, nums):
        sum = 0
        max_sub_sum = nums[0]
        for num in nums:
            sum += num
            if sum > max_sub_sum:
                max_sub_sum = sum
            if sum < 0:
                sum = 0
        return max_sub_sum