剑指offer-替换空格

FROM:http://www.nowcoder.com/books/coding-interviews/4060ac7e3e404ad1a894ef3e17650423

实现一个函数，将一个字符串中的空格替换成“%20”。例如，当字符串为We Are Happy.则经过替换之后的字符串为We%20Are%20Happy。

class Solution {
public:
  string replaceSpace(string str) {
        string rep = "%20";
        int pos = 0;
        while(pos<str.size())
            {
            if(str[pos]==' ')
                {
                str.replace(pos,1,rep);
                pos+=2;
            }else
                {
                pos+=1;
            }
        }
        return str;
  }
};