题解 | #找出字符串中第一个只出现一次的字符#

分情况讨论：存在和不存在，分别输出

while True:
    try:
        a=input()
        if(len(a)>1):
           for i in range(len(a)):
               if(i==0):
                    b1=a[1:]
                    if a[i] in b1:
                         continue
                    else:
                        print(a[0])
                        break
               else:
                  b=a[0:i]+a[i+1:]
                  if a[i] in b:
                     continue
                  else:
                     print(a[i])
                     break
           c=0
           for i in range(len(a)):
               if(i==0):
                    b2=a[1:]
                    if not a[i] in b2:
                         break
                    else:
                         c+=1
               else:
                  b2=a[0:i]+a[i+1:]
                  if not a[i] in b2:
                     break
                  else:
                     c+=1
           if(c==len(a)):
                print(-1)
        else:
            print(a)
    except:
        break