# coding=utf-8
#左旋转就是分成两部分，完成3次反转即可
def leftrotate(s,n):
    if len(s)<=0 or len(s)<n or n<0:
        return ''
    strlist=list(s)
    strlist=reverse(strlist)
    length=len(s)
    p=length-n
    frontlist=reverse(strlist[:p])
    behindlist=reverse(strlist[p:])
    resultstr=''.join(frontlist)+''.join(behindlist)
    return resultstr
def reverse(lists):
    if lists==None or len(lists)<=0:
        return ''
    startindex = 0
    endindex = len(lists) - 1
    while startindex < endindex:
        lists[startindex], lists[endindex] = lists[endindex], lists[startindex]
        startindex += 1
        endindex -= 1
    return lists
if __name__ == '__main__':
    s='abcdef'
    print(leftrotate(s,2))