日课

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