剑指5：替换空格

1.python方法：把字符创转为list，然后遇到空格就把空格换为%20，最后合成字符串

# -*- coding:utf-8 -*-
class Solution:
    # s 源字符串
    def replaceSpace(self, s):
        # write code here
        s = list(s)
        count=len(s)
        for i in range(0,count):
            if s[i]==' ':
                s[i]='%20'
        return ''.join(s)

2.统计出空格个数，算出替换后字符串长度，从后向前一次插入

# -*- coding:utf-8 -*-
class Solution:
    # s 源字符串
    def replaceSpace(self, s):
        # write code here        
        blank = 0
        n = len(s)-1
        if s == None or n <= 0:
            return
        for i in range(n):
            if s[i] == ' ':
                blank += 1 
        newn = n + blank*2
        s1 = [0]*newn
        while n > 0 and newn > n:
            if s[n] == ' ':
                s1[newn] = '0'
                newn -= 1
                s1[newn] = '2'
                newn -= 1
                s1[newn] = '%'
                newn -= 1
            else:
                s1[newn] = s[n]
            newn -= 1
            n -= 1
        s2 = ''.join(s1)
        return s2