日课

15，三数之和  ————双指针

class solution():
    def threeSum(self,nums):
        """
        :param nums: list[int]
        :return:
        """
        nums.sort()
        res = []
        for i in range(len(nums)-2):
            if nums[i]>0:
                break
            left,right = i+1,len(nums)-1
            if nums[i] + nums[left] +nums[left+1] >0 or nums[i] + nums[right-1]+nums[right] <0:
                continue
            while left < right:
                ident = nums[i] + nums[left] + nums[right]
                if ident == 0:
                    res.append([nums[i],nums[left],nums[right]])
                    left += 1
                    right -= 1
                elif ident <0:
                    left += 1
                elif ident >0:
                    right -= 1
        return res
# [[-2, -1, 3], [-2, 0, 2], [-2, 1, 1]]

7、整数反转，字符反序输出：

class reverse:
    def reverse(self,x):
        if x < (-2**31) or (x > 2**31 -1):
            return 0
        elif x >= 0:
            return int(str(x)[::-1])
        else:
            return int(str(x)[1:][::-1])*-1

3、无重复的字符子串

class solution:
    def lengthoflongestSubstring(self,s):
        st = {}
        i,ans = 0,0
        for j in range(len(s)):
            if s[j] in st:
                i = max(st[s[j]],i)
            ans = max(ans,j-i+1)
            st[s[j]] = j+1
        return ans