#!/usr/bin/env python
# -*-coding:utf-8-*-
import sys
""" 
/* 
* @Author: zuofanxiu
* @Date: 11/12/18 1:33 AM 
* @file:removeKDigits.py
* @Software: PyCharm
* 依次局部最优解->全局最优解
*/
 """

'''
@param(string): num, a positive interger which has n digits, num is a string
@param(int): k ,a positive interger
@option: remove k digit from num and make num minimize
@return(string): a new num
方法一的复杂度为o(kn)
'''

def removeZero(num):
    for i in xrange(len(num)):
        if num[i] !='0':
            break
        else:
            num = num[1:]
    return num


def func1(num, k):
    for i in xrange(k):
        hasCut = False
        for j in xrange(len(num)):
            if num[j] > num[j+1]:
                num = num[1:]
                hasCut = True
                break
        if hasCut == False:
            num = num[:len(num)-1]
        num = removeZero(num)
    if len(num) == 0:
        return "0"
    return num

def func2(num, k):
    '''
    借助栈结构, 一次遍历,遇到需要删除的数据直接出栈
    '''
    import stack
    s = stack.Stack()
    s1 = stack.Stack()
    for i in xrange(len(num)):
        while s.getTop() is not None and s.getTop() > num[i] and k > 0:
            s.pop()
            k -= 1
        s.push(num[i])
    # 字符串重组
    tmp = []
    while s.top != None:
        tmp.append(s.getTop())
        s.top = s.top.next
    res = removeZero(''.join(reversed(tmp)))
    return res



def main():
    # res = func1("1593212", 3)
    # print res
    print func2("1593212", 3)

if __name__ == '__main__':
    sys.exit(main())
复制

#!/usr/bin/env python
# -*-coding:utf-8-*-
import sys
""" 
/* 
* @Author: zuofanxiu
* @Date: 11/12/18 3:21 AM 
* @file:stack.py
* @Software: PyCharm
*/
 """
class Node(object):
    def __init__(self, val):
        self.val = val
        self.next = None


class Stack(object):
    def __init__(self):
        self.top =None

    def getTop(self):
        if self.top != None:
            return self.top.val
        else:
            return None

    def push(self, val):
        node = Node(val)
        node.next = self.top
        self.top = node
        return node.val

    def pop(self):
        if self.top == None:
            return None
        else:
            tmp = self.top.val
            self.top = self.top.next
            return tmp

    def foreach(self):
        while self.top != None:
            print self.getTop()
            self.top = self.top.next


def main():
    s = Stack()
    print s.getTop()
    s.push(1)
    s.push(2)
    s.push(3)
    # s.pop()
    print s.getTop()
    s.foreach()

if __name__ == '__main__':
    sys.exit(main())复制