Description
Write a method to replace all spaces in a string with %20. The string is given in a characters array, you can assume it has enough space for replacement and you are given the true length of the string.
You code should also return the new length of the string after replacement.
If you are using Java or Python，please use characters array instead of string.
Example
Given "Mr John Smith", length = 13.
The string after replacement should be "Mr%20John%20Smith", you need to change the string in-place and return the new length 17.
Challenge
Do it in-place.
解题：给一个字符数组，原地将空格换成 %20 。因为是原地转换，不能申请额外的空间，那么只能一步一步往后移动了。因为是把空格转换成“%20”，空格原本占用一个单位，现在需要占用三个单位，只要把原来空格的后面所有的数都向后移动两格即可。在移动的过程中，length也随之变化。代码如下：
1 public class Solution {
2 /*
3 * @param string: An array of Char
4 * @param length: The true length of the string
5 * @return: The true length of new string
6 */
7 public int replaceBlank(char[] string, int length) {
8 // write your code here
9 for(int i = 0; i < length; ){
10 //如果发现空格
11 if(string[i] == ' '){
12 for(int j = length-1; j >= i+1; j--){
13 string[j+2] = string[j];
14 }
15 string[i++] = '%';
16 string[i++] = '2';
17 string[i++] = '0';
18 length = length+2;
19 }else{
20 i++;
21 }
22 }
23 return length;
24 }
25 }